scsi: qla2xxx: Add function call to qpair for door bell

Add call back to door bell for qpair. This help reduce access to
qla_hw_data structure, in order to reduce cach thrash.

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>