[SCSI] bfa: off by one in bfa_ioc_mbox_isr()

If mc == BFI_MC_MAX then we're reading past the end of the
mod->mbhdlr[] array.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Krishna Gudipati <kgudipat@brocade.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>