video: s3c-fb: add "drop through" comment

This patch adds a "drop through" comment to improve
the readability.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
diff --git a/drivers/video/s3c-fb.c b/drivers/video/s3c-fb.c
index 8a0f022..9cee67c 100644
--- a/drivers/video/s3c-fb.c
+++ b/drivers/video/s3c-fb.c
@@ -288,6 +288,7 @@
 		/* 666 with one bit alpha/transparency */
 		var->transp.offset	= 18;
 		var->transp.length	= 1;
+		/* drop through */
 	case 18:
 		var->bits_per_pixel	= 32;