scsi: lpfc: Fix rpi release when deleting vport

A prior use-after-free mailbox fix solved it's problem by null'ing a ndlp
pointer.  However, further testing has shown that this change causes a
later state change to occasionally be skipped, which results in a reference
count never being decremented thus the rpi is never released, which causes
a vport delete to never succeed.

Revise the fix in the prior patch to no longer null the ndlp. Instead the
RELEASE_RPI flag is set which will drive the release of the rpi.

Given the new code was added at a deep indentation level, refactor the code
block using a new routine that avoids the indentation issues.

Fixes: 	9b164068

 ("scsi: lpfc: Fix use-after-free mailbox cmd completion")
Link: https://lore.kernel.org/r/20190922035906.10977-6-jsmart2021@gmail.com
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>