cfg80211: make device_type const

Instances of struct device_type are never modified, make them const.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/wireless/core.c b/net/wireless/core.c
index d89dee2..b5ff39a 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -737,7 +737,7 @@
 }
 EXPORT_SYMBOL(cfg80211_unregister_wdev);
 
-static struct device_type wiphy_type = {
+static const struct device_type wiphy_type = {
 	.name	= "wlan",
 };