scsi: qla1280: Remove set but not used variable in qla1280_done()

scsi: qla1280: Remove set but not used variable in qla1280_done()

This addresses the following gcc warning with "make W=1":

drivers/scsi/qla1280.c: In function ‘qla1280_done’:
drivers/scsi/qla1280.c:1244:19: warning: variable ‘lun’ set but not used
[-Wunused-but-set-variable]
 1244 |  int bus, target, lun;
      |                   ^~~

Link: https://lore.kernel.org/r/20200907074518.2326360-2-yanaijie@huawei.com
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>