cfg80211: Fix mutex locking in reg_last_request_cell_base

should fix the following issue

	[ 3229.815012] [ BUG: lock held when returning to user space! ]
	[ 3229.815016] 3.5.0-rc7-wl torvalds#28 Tainted: G        W  O
	[ 3229.815017]
	------------------------------------------------
	[ 3229.815019] wpa_supplicant/5783 is leaving the kernel with locks still held!
	[ 3229.815022] 1 lock held by wpa_supplicant/5783:
	[ 3229.815023]  #0: (reg_mutex){+.+.+.}, at: [<fa65834d>]
	reg_last_request_cell_base+0x1d/0x60 [cfg80211]

Cc: Luis Rodriguez <mcgrof@gmail.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Tested-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/reg.c

@@ -929,11 +929,13 @@ static bool reg_request_cell_base(struct regulatory_request *request)
 
 bool reg_last_request_cell_base(void)
 {
+	bool val;
 	assert_cfg80211_lock();
 
 	mutex_lock(&reg_mutex);
-	return reg_request_cell_base(last_request);
+	val = reg_request_cell_base(last_request);
 	mutex_unlock(&reg_mutex);
+	return val;
 }
 
 #ifdef CONFIG_CFG80211_CERTIFICATION_ONUS