um: Fix the return value of elf_core_copy_task_fpregs

This function is expected to return a boolean value, which should be
true on success and false on failure.

Fixes: d1254b12 ("uml: fix x86_64 core dump crash")
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20240913023302.130300-1-tiwei.btw@antgroup.com


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