mac8211: fix struct initialisation

Sparse showed up with the following error.
net/mac80211/agg-rx.c:480:43: warning: Using plain integer as NULL pointer

Fixes: 2ab4587675 (mac80211: add support for the ADDBA extension element)
Signed-off-by: John Crispin <john@phrozen.org>
Link: https://lore.kernel.org/r/20200803084540.179908-1-john@phrozen.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/agg-rx.c

@@ -477,7 +477,7 @@ void ieee80211_process_addba_request(struct ieee80211_local *local,
 				     size_t len)
 {
 	u16 capab, tid, timeout, ba_policy, buf_size, start_seq_num;
-	struct ieee802_11_elems elems = { 0 };
+	struct ieee802_11_elems elems = { };
 	u8 dialog_token;
 	int ies_len;