x86, cpufreq: remove leftover copymask_copy()

Impact: fix potential boot crash on MAXSMP

Remove code left over by:

  50c668d6: Revert "cpumask: use work_on_cpu in acpi-cpufreq.c for drv_read

That cmd.cpumask is not allocated anymore. No impact on default !MAXSMP
kernels.

Signed-off-by: Ingo Molnar <mingo@elte.hu>