mac80211: remove redundant initialization to pointer 'hdr'

The pointer hrd is being initialized with a value that is never read
and re-assigned a little later, hence the initialization is redundant
and can be removed.

Cleans up clang warning:
net/mac80211/tx.c:1924:24: warning: Value stored to 'hdr' during its
initialization is never read
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -1921,7 +1921,7 @@ void ieee80211_xmit(struct ieee80211_sub_if_data *sdata,
 {
 	struct ieee80211_local *local = sdata->local;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
-	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
+	struct ieee80211_hdr *hdr;
 	int headroom;
 	bool may_encrypt;