V4L/DVB (13119): gspca - pac7311: remove magic value for USB_BUF_SZ

The length check in reg_w_var() function is because the buffer contents
is copied to gspca_dev->usb_buf which has the size of USB_BUF_SZ bytes as
defined in drivers/media/video/gspca/gspca.h. Replace the number with
symbol for better readability and maintainability.
Signed-off-by: Marton Nemeth <nm127@freemail.hu>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/gspca/pac7311.c

@@ -474,7 +474,7 @@ static void reg_w_var(struct gspca_dev *gspca_dev,
 			reg_w_page(gspca_dev, page3_7302, sizeof page3_7302);
 			break;
 		default:
-			if (len > 64) {
+			if (len > USB_BUF_SZ) {
 				PDEBUG(D_ERR|D_STREAM,
 					"Incorrect variable sequence");
 				return;