mac80211: don't check if key is NULL in ieee80211_key_link()

We already assume that key is not NULL and dereference it in a few
other places before we check whether it is NULL, so the check is
unnecessary.  Remove it.

Fixes: 96fc6efb ("mac80211: IEEE 802.11 Extended Key ID support")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/20190830112451.21655-8-luca@coelho.fiSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/key.c

@@ -793,7 +793,7 @@ int ieee80211_key_link(struct ieee80211_key *key,
 
 	/* Non-pairwise keys must also not switch the cipher on rekey */
 	if (!pairwise) {
-		if (key && old_key && old_key->conf.cipher != key->conf.cipher)
+		if (old_key && old_key->conf.cipher != key->conf.cipher)
 			goto out;
 	}