scsi: lpfc: Fix mbuf pool resource detected as busy at driver unload

scsi: lpfc: Fix mbuf pool resource detected as busy at driver unload

In a situation where the node state changes while a REG_LOGIN is in
progress, the LPFC_MBOXQ_t structure is cleared and reused for an
UNREG_LOGIN command to release RPI resources without first freeing the mbuf
pool resource allocated for REG_LOGIN.

Release mbuf pool resource prior to repurposing of the mailbox command
structure from REG_LOGIN to UNREG_LOGIN.

Link: https://lore.kernel.org/r/20220911221505.117655-4-jsmart2021@gmail.com
Co-developed-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>