scsi: qla2xxx: Use complete switch scan for RSCN events

This patch removes unnecessary code to handle RSCN, instead performs full
scan everytime driver receives RSCN

Fixes: d4f7a16a

 ("scsi: qla2xxx: Remove ASYNC GIDPN switch command")
Cc: stable@vger.kernel.org #4.19
Signed-off-by: Quinn Tran <qtran@marvell.com>
Signed-off-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>