overlay gd: fix build for 32-bit ARM

This commit reverts a hunk of commit 2f5f0af ("Add unconvert linter")
and adds a hint for unconvert linter to ignore excessive conversion as
it is required on 32-bit platforms (e.g. armhf).

The exact error on armhf is this:

	19:06:45 ---> Making bundle: dynbinary (in bundles/17.06.0-dev/dynbinary)
	19:06:48 Building: bundles/17.06.0-dev/dynbinary-daemon/dockerd-17.06.0-dev
	19:10:58 # github.com/docker/docker/daemon/graphdriver/overlay
	19:10:58 daemon/graphdriver/overlay/copy.go:161: cannot use stat.Atim.Sec (type int32) as type int64 in argument to time.Unix
	19:10:58 daemon/graphdriver/overlay/copy.go:161: cannot use stat.Atim.Nsec (type int32) as type int64 in argument to time.Unix
	19:10:58 daemon/graphdriver/overlay/copy.go:162: cannot use stat.Mtim.Sec (type int32) as type int64 in argument to time.Unix
	19:10:58 daemon/graphdriver/overlay/copy.go:162: cannot use stat.Mtim.Nsec (type int32) as type int64 in argument to time.Unix

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

daemon/graphdriver/overlay/copy.go

@@ -157,9 +157,10 @@ func copyDir(srcDir, dstDir string, flags copyFlags) error {
 		}
 
 		// system.Chtimes doesn't support a NOFOLLOW flag atm
+		// nolint: unconvert
 		if !isSymlink {
-			aTime := time.Unix(stat.Atim.Sec, stat.Atim.Nsec)
-			mTime := time.Unix(stat.Mtim.Sec, stat.Mtim.Nsec)
+			aTime := time.Unix(int64(stat.Atim.Sec), int64(stat.Atim.Nsec))
+			mTime := time.Unix(int64(stat.Mtim.Sec), int64(stat.Mtim.Nsec))
 			if err := system.Chtimes(dstPath, aTime, mTime); err != nil {
 				return err
 			}