p54: Fix potential concurrent access to private data

Experience with the rtl8187 driver has shown that mac80211 can make
calls to the config callback routine in rapid succession. This patch
creates a mutex that protects the private data in several of the routines
called by mac80211.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/p54/p54.h b/drivers/net/wireless/p54/p54.h
index c6f27b9..cac9a51 100644
--- a/drivers/net/wireless/p54/p54.h
+++ b/drivers/net/wireless/p54/p54.h
@@ -52,6 +52,7 @@
 	int (*open)(struct ieee80211_hw *dev);
 	void (*stop)(struct ieee80211_hw *dev);
 	int mode;
+	struct mutex conf_mutex;
 	u8 mac_addr[ETH_ALEN];
 	u8 bssid[ETH_ALEN];
 	struct pda_iq_autocal_entry *iq_autocal;