annotate poll-related wait keys

__poll_t is also used as wait key in some waitqueues.
Verify that wait_..._poll() gets __poll_t as key and
provide a helper for wakeup functions to get back to
that __poll_t value.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/select.c

@@ -212,7 +212,7 @@ static int pollwake(wait_queue_entry_t *wait, unsigned mode, int sync, void *key
 	struct poll_table_entry *entry;
 
 	entry = container_of(wait, struct poll_table_entry, wait);
-	if (key && !((unsigned long)key & entry->key))
+	if (key && !(key_to_poll(key) & entry->key))
 		return 0;
 	return __pollwake(wait, mode, sync, key);
 }