drivers: scsi: storvsc: Set srb_flags in all cases

Correctly set SRB flags for all valid I/O directions. Some IHV drivers on the
Windows host require this. The host validates the command and SRB flags
prior to passing the command down to native driver stack.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>