scsi: mptscsih: Fix read sense data size

The sense data buffer in sense_buf_pool is allocated with size of
MPT_SENSE_BUFFER_ALLOC(64) (multiplied by req_depth) while SNS_LEN(sc)(96)
is used when reading the data.  That may lead to a read from unallocated
area, sometimes from another (unallocated) page.  To fix this, limit the
read size to MPT_SENSE_BUFFER_ALLOC.

Link: https://lore.kernel.org/r/20200616150446.4840-1-thenzl@redhat.com
Co-developed-by: Stanislav Saner <ssaner@redhat.com>
Signed-off-by: Stanislav Saner <ssaner@redhat.com>
Signed-off-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>