ALSA: hdsp: silence and underflow warning

I believe this probably cannot happen, as the code suggests.  There
would have to be an kcontrol->index.id which was zero, otherwise this
would be prevented in snd_ctl_find_id().  But snd_BUG_ON() is just a
WARN() or a no-op so static checkers complain that we keep on going with
a negative offset.  Let's just handle the error as well as printing
a warning.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>