vsrc_color: use internal timebase

Avoid timescale conversion, simplify.
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavfilter/vsrc_color.c

@@ -130,6 +130,7 @@ static int color_config_props(AVFilterLink *inlink)
            is_packed_rgba ? "rgba" : "yuva");
     inlink->w = color->w;
     inlink->h = color->h;
+    inlink->time_base = color->time_base;
 
     return 0;
 }
@@ -139,7 +140,7 @@ static int color_request_frame(AVFilterLink *link)
     ColorContext *color = link->src->priv;
     AVFilterBufferRef *picref = avfilter_get_video_buffer(link, AV_PERM_WRITE, color->w, color->h);
     picref->video->pixel_aspect = (AVRational) {1, 1};
-    picref->pts                 = av_rescale_q(color->pts++, color->time_base, AV_TIME_BASE_Q);
+    picref->pts                 = color->pts++;
     picref->pos                 = -1;
 
     avfilter_start_frame(link, avfilter_ref_buffer(picref, ~0));