mptcp: token: fix unititialized variable

gcc complains about use of uninitialized 'num'. Fix it by doing the first
assignment of 'num' when the variable is declared.

Fixes: 96d890d ("mptcp: add msk interations helper")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Link: https://lore.kernel.org/r/49e20da5d467a73414d4294a8bd35e2cb1befd49.1604308087.git.dcaratti@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/token.c

@@ -291,7 +291,7 @@ struct mptcp_sock *mptcp_token_iter_next(const struct net *net, long *s_slot,
 {
 	struct mptcp_sock *ret = NULL;
 	struct hlist_nulls_node *pos;
-	int slot, num;
+	int slot, num = 0;
 
 	for (slot = *s_slot; slot <= token_mask; *s_num = 0, slot++) {
 		struct token_bucket *bucket = &token_hash[slot];