Fix the following sparse warning:

drivers/scsi/bfa/bfad.c:53:17: warning: symbol 'max_rport_logins' was
not declared. Should it be static?

Link: https://lore.kernel.org/r/20200407032202.36789-8-yanaijie@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>