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>

arch/um/drivers/hostaudio_kern.c

@@ -57,6 +57,7 @@ __uml_setup("dsp=", set_dsp, "dsp=<dsp device>\n" DSP_HELP);
 
 static int set_mixer(char *name, int *add)
 {
+	*add = 0;
 	mixer = name;
 	return 0;
 }