fix: panic in vmss cache conversion

[andyzhangx]

What type of PR is this?
/kind bug

What this PR does / why we need it:
fix: panic in vmss cache conversion

Which issue(s) this PR fixes:

Fixes #

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Special notes for your reviewer:

• current nil cache conversion panic:

panic: interface conversion: interface {} is nil, not *sync.Map
 
goroutine 79 [running]:
sigs.k8s.io/cloud-provider-azure/pkg/provider.(*ScaleSet).updateCache(0xc0004390e0?, {0xc0004390e0, 0x21}, {0xc0005fc7c3, 0x2d}, {0xc0007df8a0, 0x1b}, {0xc000f510fc, 0x4}, 0xc0000b4f50)
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/sigs.k8s.io/cloud-provider-azure/pkg/provider/azure_vmss_cache.go:334 +0x7fb
sigs.k8s.io/cloud-provider-azure/pkg/provider.(*ScaleSet).WaitForUpdateResult.func1()
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/sigs.k8s.io/cloud-provider-azure/pkg/provider/azure_controller_vmss.go:141 +0xca
sigs.k8s.io/cloud-provider-azure/pkg/provider.(*ScaleSet).WaitForUpdateResult(0xc0003ff4a0?, {0x1e6acf8?, 0xc0003ff4a0?}, 0xc000f39860?, {0xc0004390e0?, 0xc000d34b00?}, {0xc0005fc7c3?, 0x160?}, {0x1bc2561, 0xb})
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/sigs.k8s.io/cloud-provider-azure/pkg/provider/azure_controller_vmss.go:149 +0x17e
sigs.k8s.io/cloud-provider-azure/pkg/provider.(*controllerCommon).AttachDisk(0xc000400000, {0x1e6acf8, 0xc0003ff4a0}, 0x0, {0xc0005fc813, 0x4f}, {0xc0005fc780, 0xe2}, {0xc0004390e0, 0x21}, ...)
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/sigs.k8s.io/cloud-provider-azure/pkg/provider/azure_controller_common.go:274 +0x1202
sigs.k8s.io/azuredisk-csi-driver/pkg/azuredisk.(*Driver).ControllerPublishVolume(0xc000162180, {0x1e6acf8, 0xc0003ff4a0}, 0xc0004136e0)
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/pkg/azuredisk/controllerserver.go:403 +0xec6
github.com/container-storage-interface/spec/lib/go/csi._Controller_ControllerPublishVolume_Handler.func1({0x1e6acf8, 0xc0003ff4a0}, {0x1ad1e20?, 0xc0004136e0})
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/github.com/container-storage-interface/spec/lib/go/csi/csi.pb.go:5712 +0x78
sigs.k8s.io/azuredisk-csi-driver/pkg/csi-common.logGRPC({0x1e6acf8, 0xc0003ff4a0}, {0x1ad1e20?, 0xc0004136e0?}, 0xc0002f9820, 0xc00042cdb0)
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/pkg/csi-common/utils.go:80 +0x35e
github.com/container-storage-interface/spec/lib/go/csi._Controller_ControllerPublishVolume_Handler({0x1ba25a0?, 0xc000162180}, {0x1e6acf8, 0xc0003ff4a0}, 0xc000413560, 0x1cbe9b8)
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/github.com/container-storage-interface/spec/lib/go/csi/csi.pb.go:5714 +0x138
google.golang.org/grpc.(*Server).processUnaryRPC(0xc000464a80, {0x1e70998, 0xc0002b2680}, 0xc00011b440, 0xc0003fefc0, 0x2b37db0, 0x0)
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/google.golang.org/grpc/server.go:1283 +0xcfe
google.golang.org/grpc.(*Server).handleStream(0xc000464a80, {0x1e70998, 0xc0002b2680}, 0xc00011b440, 0x0)
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/google.golang.org/grpc/server.go:1620 +0xa2f
google.golang.org/grpc.(*Server).serveStreams.func1.2()
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/google.golang.org/grpc/server.go:922 +0x98
created by google.golang.org/grpc.(*Server).serveStreams.func1
    /go/src/github.com/kubernetes-sigs/azuredisk-csi-driver/vendor/google.golang.org/grpc/server.go:920 +0x28a

Release note:

fix: panic in vmss cache conversion

[k8s-ci-robot]

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This pull-request has been approved by: andyzhangx

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[andyzhangx]

/retest