cfg80211: fix compile error with CONFIG_CFG80211_DEBUGFS

If CONFIG_CFG80211_DEBUGFS is enabled and CONFIG_MAC80211_DEBUGFS is
not, compilation fails in net/wireless/debugfs.c:

net/wireless/debugfs.c: In function 'cfg80211_debugfs_drv_add':
net/wireless/debugfs.c:117: error: 'struct cfg80211_registered_device'
has no member named 'debugfs'

The debugfs filed is needed if and only if CONFIG_CFG80211_DEBUGFS is
enabled, so use that instead of CONFIG_MAC80211_DEBUGFS.
Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/core.h

@@ -51,7 +51,7 @@ struct cfg80211_registered_device {
 	struct cfg80211_scan_request *scan_req; /* protected by RTNL */
 	unsigned long suspend_at;
 
-#ifdef CONFIG_MAC80211_DEBUGFS
+#ifdef CONFIG_CFG80211_DEBUGFS
 	/* Debugfs entries */
 	struct wiphy_debugfsdentries {
 		struct dentry *rts_threshold;