scsi: megaraid_sas: make max_sectors visible in sys

Support is easier with all driver parameters visible in sysfs.

Signed-off-by: Tomas Henzl <thenzl@redhat.com>
Acked-by: Sumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>