wl12xx: fix a couple of sparse warnings about undeclared functions

Fix the following sparse warnings:

drivers/net/wireless/wl12xx/main.c:1129:5: warning: symbol '__wl1271_plt_stop' was not declared. Should it be static?
drivers/net/wireless/wl12xx/main.c:2988:5: warning: symbol 'wl1271_op_ampdu_action' was not declared. Should it be static?

Both functions should be static.
Signed-off-by: Luciano Coelho <coelho@ti.com>

drivers/net/wireless/wl12xx/main.c

@@ -1126,7 +1126,7 @@ int wl1271_plt_start(struct wl1271 *wl)
 	return ret;
 }
 
-int __wl1271_plt_stop(struct wl1271 *wl)
+static int __wl1271_plt_stop(struct wl1271 *wl)
 {
 	int ret = 0;
 
@@ -2985,7 +2985,8 @@ static int wl1271_op_sta_remove(struct ieee80211_hw *hw,
 	return ret;
 }
 
-int wl1271_op_ampdu_action(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
+static int wl1271_op_ampdu_action(struct ieee80211_hw *hw,
+				  struct ieee80211_vif *vif,
 				  enum ieee80211_ampdu_mlme_action action,
 				  struct ieee80211_sta *sta, u16 tid, u16 *ssn,
 				  u8 buf_size)