[PATCH] x86_64: Initialize powernow_data[] for all siblings

I got an oops on a dual core system because the lost tick handler
called cpufreq_get() on core 1 and powernow tried to follow
a NULL powernow_data[] pointer there.

Initialize powernow_data for all cores of a CPU.

Cc: Jacob Shin <jacob.shin@amd.com>
Cc: Dave Jones <davej@redhat.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>