lpfc: mark function as static in lpfc/lpfc_bsg.c

[PATCH 26/55] scsi: Mark function as static in lpfc/lpfc_bsg.c

Mark function as static in lpfc/lpfc_bsg.c because it is not used
outside this file.

This eliminates the following warning in lpfc/lpfc_bsg.c:
drivers/scsi/lpfc/lpfc_bsg.c:3348:1: warning: no previous prototype for ‘lpfc_bsg_issue_mbox_cmpl’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: James Smart <james.smart@emulex.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>