core: Fix API documentation bugs

data/grl-media-audio.c:180: Warning: Grl: grl_media_audio_set_mb_recording_id: unknown parameter 'mb_track_id' in documentation comment, should be 'mb_recording_id'
data/grl-media-video.c:182: Warning: Grl: grl_media_video_set_episode_title: unknown parameter 'show' in documentation comment, should be 'episode_title'