USB: gadget: udc: s3c2410_udc: Mark expected switch fall-throughs

Mark switch cases where we are expecting to fall through.

This patch fixes the following warning (Building: tct_hammer_defconfig arm):

drivers/usb/gadget/udc/s3c2410_udc.c:314:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
drivers/usb/gadget/udc/s3c2410_udc.c:418:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Link: https://lore.kernel.org/r/20190805191426.GA12414@embeddedorSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/s3c2410_udc.c

@@ -312,6 +312,7 @@ static int s3c2410_udc_write_fifo(struct s3c2410_ep *ep,
 	switch (idx) {
 	default:
 		idx = 0;
+		/* fall through */
 	case 0:
 		fifo_reg = S3C2410_UDC_EP0_FIFO_REG;
 		break;
@@ -416,6 +417,7 @@ static int s3c2410_udc_read_fifo(struct s3c2410_ep *ep,
 	switch (idx) {
 	default:
 		idx = 0;
+		/* fall through */
 	case 0:
 		fifo_reg = S3C2410_UDC_EP0_FIFO_REG;
 		break;