[CPUFREQ] Fix memory leaks in pcc_cpufreq_do_osc

If acpi_evaluate_object() function call doesn't fail, we must kfree()
output.buffer before returning from pcc_cpufreq_do_osc().

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Dave Jones <davej@redhat.com>