ACPI: processor_perflib: Simplify code and stop using CPUFREQ_START

acpi_processor_ppc_notifier() can live without using CPUFREQ_START
(which is gonna be removed soon), as it is only used while setting
ignore_ppc to 0. This can be done with the help of "ignore_ppc < 0"
check alone. The notifier function anyway ignores all events except
CPUFREQ_ADJUST and dropping CPUFREQ_START wouldn't harm at all.

Once CPUFREQ_START event is removed from the cpufreq core,
acpi_processor_ppc_notifier() will get called only for CPUFREQ_NOTIFY or
CPUFREQ_ADJUST event. Drop the return statement from the first if block
to make sure we don't ignore any such events.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>