scsi: ufs: fix bugs related to null pointer access and array size

In this change there are a few fixes of possible NULL pointer access and
possible access to index that exceeds array boundaries.

Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>