[CPUFREQ] Prevent p4-clockmod from auto-binding to the ondemand governor.

The latency of p4-clockmod sucks so hard that scaling on a regular
basis with ondemand is a really bad idea.

Signed-off-by: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: Dave Jones <davej@redhat.com>