scsi: lpfc: Fix PLOGI failure with high remoteport count

When connected to a high number of remote ports, the driver is encountering
PLOGI errors.  The errors are due to adapter detected failures indicating
illegal field values.

Turns out the driver was prematurely clearing an RPI bitmask before waiting
for an UNREG_RPI mailbox completion. This allowed the RPI to be reused
before it was actually available.

Fix by clearing RPI bitmask only after UNREG_RPI mailbox completion.

Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>