cpufreq: pcc-cpufreq: Fail initialization if driver cannot be registered

Make pcc_cpufreq_init() return error codes when the driver cannot be
registered.  Otherwise the driver can shows up loaded via lsmod even
though it failed initialization.  This is confusing to the user.

Signed-off-by: David Arcari <darcari@redhat.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>