acpi-cpufreq: De-register CPU notifier and free struct msr on error.

If cpufreq_register_driver() fails we would free the acpi driver
related structures but not free the ones allocated
by acpi_cpufreq_boost_init() function. This meant that as
the driver error-ed out and a CPU online/offline event came
we would crash and burn as one of the CPU notifiers would point
to garbage.

Fixes: cfc9c8ed

 (acpi-cpufreq: Adjust the code to use the common boost attribute)
Acked-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>