ALSA: x86: Reduce redundant register field names

Currently each register definition contains the own prefix in the
union struct itself; for example, union aud_ch_status_0 has
status_0_regx and status_0_regval fields.  These are simply
superfluous, since usually the type of the variable is seen in its
declaration or in its name.

In this patch, we cut off these prefixes.  Now all register
definitions have regx and regval fields consistently, instead.

Signed-off-by: Takashi Iwai <tiwai@suse.de>