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: d1254b12c93e ("uml: fix x86_64 core dump crash")
Signed-off-by: Tiwei Bie <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Johannes Berg <[e-mail]>

arch/um/kernel/process.c

···
 {
 	int cpu = current_thread_info()->cpu;
 
-	return save_i387_registers(userspace_pid[cpu], (unsigned long *) fpu);
+	return save_i387_registers(userspace_pid[cpu], (unsigned long *) fpu) == 0;
 }