scsi: megaraid_sas: Add helper functions for irq_context

Adding helper functions for ISR access and release to improve readability.

Link: https://lore.kernel.org/r/20210929124022.24605-3-sumit.saxena@broadcom.com


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