ALSA: usb-audio: Set the value of potential sticky mixers to maximum

ALSA: usb-audio: Set the value of potential sticky mixers to maximum

It makes no sense to restore the saved value for a sticky mixer, since
setting any value is a no-op.

However, in some rare cases, SET_CUR is effective despite GET_CUR always
returns a constant value. These mixers are not sticky, but there's no
way to distinguish them. Without any additional information, the best
thing we can do is to set the mixer value to the maximum before bailing
out, so that a soft mixer can still reach the maximum hardware volume if
the mixer turns out to be non-sticky. Meanwhile, all channels must be
synchronized to prevent imbalance volume.

Fixes: 86aa1ea1f15c ("ALSA: usb-audio: Do not expose sticky mixers")
Signed-off-by: Rong Zhang <i@rong.moe>
Link: https://patch.msgid.link/20260531-uac-sticky-error-path-v1-1-12c2329d17ef@rong.moe
Signed-off-by: Takashi Iwai <tiwai@suse.de>