iwlwifi: mvm: Avoid accessing Null pointer when setting igtk

Sometimes when setting an igtk key the station maybe NULL.
In the of case igtk the function will skip to the end, and
try to print sta->addr, if sta is Null - we will access a
Null pointer.

Avoid accessing a Null pointer when setting a igtk key &
the sta == NULL, and print a default MAC address instead.
Signed-off-by: Matti Gottlieb <matti.gottlieb@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

drivers/net/wireless/iwlwifi/mvm/sta.c

@@ -1401,6 +1401,7 @@ int iwl_mvm_set_sta_key(struct iwl_mvm *mvm,
 	bool mcast = !(keyconf->flags & IEEE80211_KEY_FLAG_PAIRWISE);
 	u8 sta_id;
 	int ret;
+	static const u8 __maybe_unused zero_addr[ETH_ALEN] = {0};
 
 	lockdep_assert_held(&mvm->mutex);
 
@@ -1467,7 +1468,7 @@ int iwl_mvm_set_sta_key(struct iwl_mvm *mvm,
 end:
 	IWL_DEBUG_WEP(mvm, "key: cipher=%x len=%d idx=%d sta=%pM ret=%d\n",
 		      keyconf->cipher, keyconf->keylen, keyconf->keyidx,
-		      sta->addr, ret);
+		      sta ? sta->addr : zero_addr, ret);
 	return ret;
 }