scsi: qla2xxx: Remove set but not used variable 'ptr_dma'

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

drivers/scsi/qla2xxx/qla_iocb.c: In function 'qla24xx_els_dcmd2_iocb':
drivers/scsi/qla2xxx/qla_iocb.c:2644:13: warning:
 variable 'ptr_dma' set but not used [-Wunused-but-set-variable]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>