um: hostaudio: Do not propagate mixer parameter to kernel

This parameter is UML specific and is unknown to kernel. It should
not be propagated to kernel, otherwise it will trigger a warning and
be passed to user space as an environment option.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20241011040441.1586345-9-tiwei.btw@antgroup.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>