usb: image: mdc800: mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/image/mdc800.c

@@ -893,6 +893,7 @@ static ssize_t mdc800_device_write (struct file *file, const char __user *buf, s
 						return -EIO;
 					}
 					mdc800->pic_len=-1;
+					/* fall through */
 
 				case 0x09: /* Download Thumbnail */
 					mdc800->download_left=answersize+64;