scsi: qla2xxx: Fix re-login for Nport Handle in use

When NPort Handle is in use, driver needs to mark the handle as used and
pick another. Instead, the code clears the handle and re-pick the same
handle.

Fixes: 726b8548 ("qla2xxx: Add framework for async fabric discovery")
Cc: <stable@vger.kernel.org> # 4.10+
Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>