[CPUFREQ] bugfix cpufreq in combination with performance governor

There is a frequency scaling issue that I encountered with the performance
governor in combination with CPU hotplug.

In cpufreq.c CPU frequency is reduced to its minimum before the CPU gets
unregistered and set offline.  Does that have a particular reason?

Since the (k8-)governor does not monitor CPU frequency that setting also
applies then to the remaining CPU as well and lets the system run on the
lowest frequency although performance is chose as the policy.

Signed-off-by: Peter Oruba <peter.oruba@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Jones <davej@redhat.com>