[CPUFREQ] powernow-k8: check space_id of _PCT registers to be FFH

The powernow-k8 driver checks to see that the Performance Control/Status
Registers are declared as FFH (functional fixed hardware) by the BIOS.
However, this check got broken in the commit:
 0e64a0c9
 [CPUFREQ] checkpatch cleanups for powernow-k8

Fix based on an original patch from Naga Chumbalkar.

Signed-off-by: Naga Chumbalkar <nagananda.chumbalkar@hp.com>
Cc: Mark Langsdorf <mark.langsdorf@amd.com>
Signed-off-by: Dave Jones <davej@redhat.com>