ALSA: hda - Check leaf nodes to find aamix amps

The current generic parser assumes blindly that the volume and mute
amps are found in the aamix node itself.  But on some codecs,
typically Analog Devices ones, the aamix amps are separately
implemented in each leaf node of the aamix node, and the current
driver can't establish the correct amp controls.  This is a regression
compared with the previous static quirks.

This patch extends the search for the amps to the leaf nodes for
allowing the aamix controls again on such codecs.
In this implementation, I didn't code to loop through the whole paths,
since usually one depth should suffice, and we can't search too
deeply, as it may result in the conflicting control assignments.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=65641


Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>