scsi: ufs: validate input args to queuecommand

Make sure to validate the input args to queuecommand to avoid
NULL dereferences.

Change-Id: I803e1cc019a4c5569fed9ee08113e323daab75c8
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
[cang@codeaurora.org: resolved trivial merge conflicts and
fixed kernel compilation error by removing cmd_type checking]
Signed-off-by: Can Guo <cang@codeaurora.org>