um: Always dump trace for specified task in show_stack

Currently, show_stack() always dumps the trace of the current task.
However, it should dump the trace of the specified task if one is
provided. Otherwise, things like running "echo t > sysrq-trigger"
won't work as expected.

Fixes: 970e51fe ("um: Add support for CONFIG_STACKTRACE")
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20241106103933.1132365-1-tiwei.btw@antgroup.com


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