cpufreq: ACPI: Use on_each_cpu_mask() in drv_write()

Make drv_write() call on_each_cpu_mask() instead of using an open-coded
equivalent of the latter.

Also remove a comment mentioning the smp_call_function_many() usage
which is not particularly useful anyway.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>