megaraid_sas: Code refactor for use of requestorId

Some of these code changes were proposed by David Binderman.

Removed redudant check of requestorId. Redundant condition:
instance.requestorId. Check for plasma firmware 1.11 are now
restructured to support only specific device id.

Signed-off-by: Sumit Saxena <sumit.saxena@avagotech.com>
Signed-off-by: Kashyap Desai <kashyap.desai@avagotech.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>