drm/exynos: mixer: fix chroma comment in vp_video_buffer()

The current comment sounds like the division op is done to
compensate for some hardware erratum. But the chroma plane
having half the height of the luma plane is just the way
NV12/NV21 is defined, so clarify this behaviour.
Signed-off-by: NTobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: NInki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_mixer.c

@@ -532,7 +532,7 @@ static void vp_video_buffer(struct mixer_context *ctx,
 	/* setting size of input image */
 	vp_reg_write(res, VP_IMG_SIZE_Y, VP_IMG_HSIZE(fb->pitches[0]) |
 		VP_IMG_VSIZE(fb->height));
-	/* chroma height has to reduced by 2 to avoid chroma distorions */
+	/* chroma plane for NV12/NV21 is half the height of the luma plane */
 	vp_reg_write(res, VP_IMG_SIZE_C, VP_IMG_HSIZE(fb->pitches[0]) |
 		VP_IMG_VSIZE(fb->height / 2));