staging: rtl8188eu: make sta2sta_data_frame() static

Function sta2sta_data_frame() is only used in rtw_recv.c.
So make it static.
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/core/rtw_recv.c

@@ -632,7 +632,8 @@ static void count_rx_stats(struct adapter *padapter,
 	}
 }
 
-int sta2sta_data_frame(struct adapter *adapter, struct recv_frame *precv_frame,
+static int sta2sta_data_frame(struct adapter *adapter,
+			      struct recv_frame *precv_frame,
 			      struct sta_info **psta)
 {
 	int ret = _SUCCESS;