mt76: mt7915: add missing CONFIG_MAC80211_DEBUGFS

Add CONFIG_MAC80211_DEBUGFS to fix a reported warning.

Fixes: ec9742a8 ("mt76: mt7915: add .sta_add_debugfs support")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c

@@ -391,6 +391,7 @@ int mt7915_init_debugfs(struct mt7915_dev *dev)
 	return 0;
 }
 
+#ifdef CONFIG_MAC80211_DEBUGFS
 /** per-station debugfs **/
 
 /* usage: <tx mode> <ldpc> <stbc> <bw> <gi> <nss> <mcs> */
@@ -468,3 +469,4 @@ void mt7915_sta_add_debugfs(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 	debugfs_create_file("fixed_rate", 0600, dir, sta, &fops_fixed_rate);
 	debugfs_create_file("stats", 0400, dir, sta, &fops_sta_stats);
 }
+#endif