-tip testing found this crash:

> [   35.258515] calling  acpi_cpufreq_init+0x0/0x127 @ 1
> [   35.264127] BUG: unable to handle kernel NULL pointer dereference at (null)
> [   35.267554] IP: [<ffffffff80478092>] __bitmap_intersects+0x48/0x73
> [   35.267554] PGD 0
> [   35.267554] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC

arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c is still broken: there's no
allocation of the variable mask, so we pass in an uninitialized cmd.mask
field to drv_read(), which then passes it to the scheduler which then
crashes ...

Switch it over to the much simpler constant-cpumask-pointers approach.
Signed-off-by: Ingo Molnar <mingo@elte.hu>