[CPUFREQ] Fix sparse warning in powernow-k8

arch/x86/kernel/cpu/cpufreq/powernow-k8.c:1238:9: warning: symbol '__ptr' shadows an earlier one
arch/x86/kernel/cpu/cpufreq/powernow-k8.c:1238:9: originally declared here

Signed-off-by: Dave Jones <davej@redhat.com>