qla2xxx: Remove a superfluous test

Avoid that smatch reports the following warning:

drivers/scsi/qla2xxx/qla_attr.c:1081: qla2x00_model_desc_show() warn: this array is probably non-NULL. 'vha->hw->model_desc'

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Acked-by: Himanshu Madhani <himanshu.madhani@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>