ALSA: hda - rename function not_share_unassigned_cvt()

The function name not_share_unassigned_cvt() is opposite to what it does.
This patch renames it to intel_not_share_assigned_cvt(), and addes comments
to explain why some Intel display codecs need this workaround.

Signed-off-by: Mengdong Lin <mengdong.lin@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>