afs: Fix use of BUG()

Fix afs_compare_addrs() to use WARN_ON(1) instead of BUG() and return 1
(ie. srx_a > srx_b).

There's no point trying to put actual error handling in as this should not
occur unless a new transport address type is allowed by AFS.  And even if
it does, in this particular case, it'll just never match unknown types of
addresses.  This BUG() was more of a 'you need to add a case here'
indicator.
Reported-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

fs/afs/vl_alias.c

@@ -73,7 +73,8 @@ static int afs_compare_addrs(const struct sockaddr_rxrpc *srx_a,
 	}
 
 	default:
-		BUG();
+		WARN_ON(1);
+		diff = 1;
 	}
 
 out: