doc: Fix documentation for grl_media_get_player()
doc: Fix documentation for grl_media_get_player()

Documentation was referring to grl_media_get_external_player() instead of
grl_media_get_player().

jasuarez/grilo,MathieuDuponchelle/grilo,GNOME/grilo,GNOME/grilo,kyoushuu/grilo,kyoushuu/grilo,kyoushuu/grilo,MathieuDuponchelle/grilo,grilofw/grilo,kyoushuu/grilo,grilofw/grilo,jasuarez/grilo,jasuarez/grilo,MathieuDuponchelle/grilo,grilofw/grilo