scsi: lpfc: Refactor and clean up mailbox command memory free

A lot of repeated clean up code exists when freeing mailbox commands in
lpfc_mem_free_all().

Introduce a lpfc_mem_free_sli_mbox() helper routine to refactor the
copy-paste code.  Additionally, reinitialize the mailbox command structure
context pointers to NULL in lpfc_sli4_mbox_cmd_free().

Signed-off-by: Justin Tee <justin.tee@broadcom.com>
Link: https://lore.kernel.org/r/20231031191224.150862-7-justintee8345@gmail.com


Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>