scsi: hisi_sas: remove set but not used variable 'irq_value'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/scsi/hisi_sas/hisi_sas_v1_hw.c: In function cq_interrupt_v1_hw:
drivers/scsi/hisi_sas/hisi_sas_v1_hw.c:1542:6: warning: variable irq_value set but not used [-Wunused-but-set-variable]

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Acked-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>