[videosink] Rename the use_shader property to use-shader
[videosink] Rename the use_shader property to use-shader

This does not change the API as properties' names are canonicalized.
From GOject's manual: parameter names need to start with a letter
(a-z or A-Z). Subsequent characters can be letters, numbers or a '-'.
All other characters are replaced by a '-' during construction.

ystreet/clutter-gst,lubosz/clutter-gst,GNOME/clutter-gst,lubosz/clutter-gst,skinkie/clutter-gst,skinkie/clutter-gst,lubosz/clutter-gst,ystreet/clutter-gst,GNOME/clutter-gst,ystreet/clutter-gst,ystreet/clutter-gst,skinkie/clutter-gst,GNOME/clutter-gst,GNOME/clutter-gst