scsi: ufs: fix sense buffer size to 18 bytes

According to UFS device specification, sense data can be only 18 bytes
long, this change makes the changes accordingly.

Signed-off-by: Gilad Broner <gbroner@codeaurora.org>
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>