avfilter/vf_colorspace_cuda: mark fall-through

libavfilter/vf_colorspace_cuda.c

@@ -281,6 +281,7 @@ static int conv_cuda_convert(AVFilterContext* ctx, AVFrame* out, AVFrame* in)
             break;
         case AV_PIX_FMT_YUV420P:
             width = comp_id ? in->width / 2 : in->width;
+            /* fall-through */
         case AV_PIX_FMT_NV12:
             height = comp_id ? in->height / 2 : in->height;
             break;