vsrc_color: add @file doxy

Also remove outdated reference to color in vf_pad.c.

libavfilter/vf_pad.c

@@ -21,7 +21,7 @@
 
 /**
  * @file
- * video padding filter and color source
+ * video padding filter
  */
 
 #include "avfilter.h"

libavfilter/vsrc_color.c

@@ -18,6 +18,11 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+/**
+ * @file
+ * color source
+ */
+
 #include "avfilter.h"
 #include "libavutil/pixdesc.h"
 #include "libavutil/colorspace.h"