cw1200: Fix memory leak in cw1200_set_key()

When wsm_key.index > WSM_KEY_MAX_INDEX, cw1200_set_key() returns without
calling cw1200_free_key() like other wrong paths, which may lead to a
potential memory leak.

We can fix it by calling cw1200_free_key() when some error occurs.

Signed-off-by: Jianglei Nie <niejianglei2021@163.com>

drivers/net/wireless/st/cw1200/sta.c

@@ -823,6 +823,7 @@ int cw1200_set_key(struct ieee80211_hw *dev, enum set_key_cmd cmd,
 		};
 
 		if (wsm_key.index > WSM_KEY_MAX_INDEX) {
+			cw1200_free_key(priv, idx);
 			ret = -EINVAL;
 			goto finally;
 		}