scsi: qla1280: Remove set but not used variable in qla1280_mailbox_command()

scsi: qla1280: Remove set but not used variable in qla1280_mailbox_command()

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

drivers/scsi/qla1280.c: In function ‘qla1280_mailbox_command’:
drivers/scsi/qla1280.c:2430:11: warning: variable ‘data’ set but not
used [-Wunused-but-set-variable]
 2430 |  uint16_t data;
      |           ^~~~

Link: https://lore.kernel.org/r/20200907074518.2326360-4-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>