staging: r8188eu: remove needless check before usb_free_urb()

usb_free_urb(NULL) is safe and this check is not required.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/os_dep/recv_linux.c

@@ -77,8 +77,7 @@ int rtw_os_recvbuf_resource_alloc(struct adapter *padapter,
 int rtw_os_recvbuf_resource_free(struct adapter *padapter,
 				 struct recv_buf *precvbuf)
 {
-	if (precvbuf->purb)
-		usb_free_urb(precvbuf->purb);
+	usb_free_urb(precvbuf->purb);
 	return _SUCCESS;
 }