ext/flac/gstflacenc.c: Make sure the desired default values are actually set, not only registered as defaults (actual...

Original commit message from CVS:
* ext/flac/gstflacenc.c: (gst_flac_enc_class_init):
Make sure the desired default values are actually set, not only
registered as defaults (actual problem is that the stereo-specific
values are only updated if channels==2, which is not the case yet
when the object is created, so the default values for the
mid-side-stereo and loose-mid-side-stereo settings are never
set in _update_quality()). Makes flacenc create smaller files by
default (for stereo input), and fixes #550791.