mac80211: use offsetofend()

This was created using the following spatch:
    @find@
    type S;
    expression M, M2;
    position p;
    @@
    offsetof(S, M) + sizeof(M2)@p

    @script:python@
    m << find.M;
    m2 << find.M2;
    @@
    if not m2.endswith('-> ' + m):
            cocci.include_match(False)

    @change@
    type find.S;
    expression find.M, find.M2;
    position find.p;
    @@
    -offsetof(S, M) + sizeof(M2)@p
    +offsetofend(S, M)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index bfecc3e..d57e5f6 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -2977,8 +2977,8 @@ int ieee80211_send_action_csa(struct ieee80211_sub_if_data *sdata,
 	struct ieee80211_mgmt *mgmt;
 	struct ieee80211_local *local = sdata->local;
 	int freq;
-	int hdr_len = offsetof(struct ieee80211_mgmt, u.action.u.chan_switch) +
-			       sizeof(mgmt->u.action.u.chan_switch);
+	int hdr_len = offsetofend(struct ieee80211_mgmt,
+				  u.action.u.chan_switch);
 	u8 *pos;
 
 	if (sdata->vif.type != NL80211_IFTYPE_ADHOC &&