SELinux: silence build warning when !CONFIG_BUG

If one builds a kernel without CONFIG_BUG there are a number of 'may be
used uninitialized' warnings.  Silence these by returning after the BUG().

Signed-off-by: Eric Paris <eparis@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>

security/selinux/netnode.c

@@ -141,6 +141,7 @@ static struct sel_netnode *sel_netnode_find(const void *addr, u16 family)
 		break;
 	default:
 		BUG();
+		return NULL;
 	}
 
 	list_for_each_entry_rcu(node, &sel_netnode_hash[idx].list, list)