video: Handle the 'bell' character

This can be sent when to many characters are entered. Make sure it is
ignored and does not cause a character to be displayed.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/video.c b/test/dm/video.c
index be94633..4e3f9d5 100644
--- a/test/dm/video.c
+++ b/test/dm/video.c
@@ -124,7 +124,7 @@
 static int dm_test_video_chars(struct unit_test_state *uts)
 {
 	struct udevice *dev, *con;
-	const char *test_string = "Well\b\b\b\bxhe is\r \n\ta very modest  \bman\n\t\tand Has much to\b\bto be modest about.";
+	const char *test_string = "Well\b\b\b\bxhe is\r \n\ta very \amodest  \bman\n\t\tand Has much to\b\bto be modest about.";
 	const char *s;
 
 	ut_assertok(uclass_get_device(UCLASS_VIDEO, 0, &dev));