[CPUFREQ] x86_64: Proper null pointer check in powernow_k8_get

This prevents crashes on dual core system when enough ticks are lost.

Replaces earlier patch by me.

(Duplicate null data check in powernowk8_get() removed -- davej)

 arch/i386/kernel/cpu/cpufreq/powernow-k8.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Dave Jones <davej@redhat.com>