scsi: storvsc: Prefer kcalloc over kzalloc with multiply

Use kcalloc for allocating an array instead of kzalloc with multiply,
kcalloc is the preferred API.

Found with checkpatch.

Signed-off-by: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>