Staging: rtl8192 Clean up function definition

Change function definition to match its prototype declaration. This
fixes the following warning generated by sparse:

drivers/staging/rtl8192u/r8192U_core.c:1970:6: warning: symbol
'rtl8192_update_ratr_table' was not declared. Should it be static?
Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192u/r8192U_core.c

@@ -1967,7 +1967,7 @@ static int rtl8192_handle_assoc_response(struct net_device *dev,
 }
 
 
-void rtl8192_update_ratr_table(struct net_device *dev)
+static void rtl8192_update_ratr_table(struct net_device *dev)
 {
 	struct r8192_priv *priv = ieee80211_priv(dev);
 	struct ieee80211_device *ieee = priv->ieee80211;