media: mediatek: vcodec: decoder: Const-ify stepwise_fhd

stepwise_fhd is the reference framesize variable, and should not be
altered. Make it constant.

Fixes: ("76250b48 media: mediatek: vcodec: Getting supported decoder format types")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec_stateless.c

@@ -119,7 +119,7 @@ static struct mtk_video_fmt default_cap_format;
 static unsigned int num_formats;
 static unsigned int num_framesizes;
 
-static struct v4l2_frmsize_stepwise stepwise_fhd = {
+static const struct v4l2_frmsize_stepwise stepwise_fhd = {
 	.min_width = MTK_VDEC_MIN_W,
 	.max_width = MTK_VDEC_MAX_W,
 	.step_width = 16,