tests/qemu-iotests: Fix 051 for binaries without 'lsi53c895a'

The lsi53c895a SCSI adaptor might not be enabled in each and every
x86 QEMU binary, e.g. it's disabled in the RHEL/CentOS build.
Thus let's add a check to the 051 test so that it does not fail if
this device is not available.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20211206143404.247032-1-thuth@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

tests/qemu-iotests/051

@@ -45,6 +45,10 @@ _supported_proto file
 _unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file
 _require_drivers nbd
 
+if [ "$QEMU_DEFAULT_MACHINE" = "pc" ]; then
+    _require_devices lsi53c895a
+fi
+
 do_run_qemu()
 {
     echo Testing: "$@"