staging: rtl8188eu: remove unnecessary declaration

The declaration of sta2sta_data_frame() is directly above
the function definition. Remove the unnecessary declaration.

This also clears a checkpatch issue.
CHECK: Lines should not end with a '('
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

@@ -632,12 +632,6 @@ static void count_rx_stats(struct adapter *padapter,
 	}
 }
 
-int sta2sta_data_frame(
-	struct adapter *adapter,
-	struct recv_frame *precv_frame,
-	struct sta_info **psta
-);
-
 int sta2sta_data_frame(struct adapter *adapter, struct recv_frame *precv_frame,
 		       struct sta_info **psta)
 {