storvsc: Set the SRB flags correctly when no data transfer is needed

Set the SRB flags correctly when there is no data transfer.  Without this
change some IHV drivers will fail valid commands such as TEST_UNIT_READY.

Cc: <stable@vger.kernel.org>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Long Li <longli@microsoft.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>