scsi: lpfc: Fix crash in target side cable pulls hitting WAIT_FOR_UNREG

Kernel is crashing with the following stacktrace:

  BUG: unable to handle kernel NULL pointer dereference at
    00000000000005bc
  IP: lpfc_nvme_register_port+0x1a8/0x3a0 [lpfc]
  ...
  Call Trace:
  lpfc_nlp_state_cleanup+0x2b2/0x500 [lpfc]
  lpfc_nlp_set_state+0xd7/0x1a0 [lpfc]
  lpfc_cmpl_prli_prli_issue+0x1f7/0x450 [lpfc]
  lpfc_disc_state_machine+0x7a/0x1e0 [lpfc]
  lpfc_cmpl_els_prli+0x16f/0x1e0 [lpfc]
  lpfc_sli_sp_handle_rspiocb+0x5b2/0x690 [lpfc]
  lpfc_sli_handle_slow_ring_event_s4+0x182/0x230 [lpfc]
  lpfc_do_work+0x87f/0x1570 [lpfc]
  kthread+0x10d/0x130
  ret_from_fork+0x35/0x40

During target side fault injections, it is possible to hit the
NLP_WAIT_FOR_UNREG case in lpfc_nvme_remoteport_delete. A prior commit
fixed a rebind and delete race condition, but called lpfc_nlp_put
unconditionally. This triggered a deletion and the crash.

Fix by movng nlp_put to inside the NLP_WAIT_FOR_UNREG case, where the nlp
will be being unregistered/removed. Leave the reference if the flag isn't
set.

Link: https://lore.kernel.org/r/20200322181304.37655-8-jsmart2021@gmail.com
Fixes: b15bd3e6

 ("scsi: lpfc: Fix nvme remoteport registration race conditions")
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>