[mutter] cogl: Fix cogl_frame_info_get_frame_counter docs

[Jonas Ådahl <jadahl src gnome org>]

commit c6691afa3842d2863aff17c83a4d96fd27140cf1
Author: Daniel van Vugt <daniel van vugt canonical com>
Date:   Thu Jun 28 15:46:47 2018 +0800

    cogl: Fix cogl_frame_info_get_frame_counter docs
    
    The docs previously suggested that `cogl_frame_info_get_frame_counter`
    returned a timestamp of an unknown clock ID. That's not correct. The
    cogl source code shows that it does and must use the same clock as
    `cogl_get_clock_time`.
    
    Related to https://gitlab.gnome.org/GNOME/mutter/issues/131

 cogl/cogl/cogl-frame-info.h | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)
---
diff --git a/cogl/cogl/cogl-frame-info.h b/cogl/cogl/cogl-frame-info.h
index a87f7e13b..1d93476a1 100644
--- a/cogl/cogl/cogl-frame-info.h
+++ b/cogl/cogl/cogl-frame-info.h
@@ -89,11 +89,8 @@ int64_t cogl_frame_info_get_frame_counter (CoglFrameInfo *info);
  * Gets the presentation time for the frame. This is the time at which
  * the frame became visible to the user.
  *
- * The presentation time measured in nanoseconds is based on a
- * monotonic time source. The time source is not necessarily
- * correlated with system/wall clock time and may represent the time
- * elapsed since some undefined system event such as when the system
- * last booted.
+ * The presentation time measured in nanoseconds, is based on
+ * cogl_get_clock_time().
  *
  * <note>Linux kernel version less that 3.8 can result in
  * non-monotonic timestamps being reported when using a drm based