ALSA: hdac: Fix codec name after machine driver is unloaded and reloaded

Currently on each driver reload internal counter is being increased. It
causes failure to enumerate driver devices, as they have hardcoded:
.codec_name = "ehdaudio0D2",
As there is currently no devices with multiple hda codecs and there is
currently no established way to reliably differentiate, between them,
always assign bus->idx = 0;

This fixes a problem when we unload and reload machine driver idx gets
incremented, so .codec_name would've needed to be set to "ehdaudio1D2"
after first reload and so on.

Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>