um: Do not propagate initrd parameter to kernel

This parameter is UML specific. It specifies the name of the file
containing the initrd image, which is unknown to kernel.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20241011040441.1586345-10-tiwei.btw@antgroup.com


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