cogl-pango-fontmap: Use the right unref function for the renderer
cogl-pango-fontmap: Use the right unref function for the renderer

The renderer was being unrefed with cogl_object_unref but it's
actually a GObject.

Reviewed-by: Robert Bragg <12e9293ec6b30c7fa8a0926af42807e929c1684f@linux.intel.com>

djdeath/cogl,djdeath/cogl-android,djdeath/cogl-android,gcampax/cogl,gcampax/cogl,gcampax/cogl,djdeath/cogl-android,gcampax/cogl,djdeath/cogl,djdeath/cogl