[CPUFREQ] Longhaul - Proper register access

In previous commit I used u32 for u16 register.
This code will work only when ACPI block address is set.
For now it is only for VT8235 and VT8237.

Signed-off-by: Rafal Bilski <rafalbilski@interia.pl>
Signed-off-by: Dave Jones <davej@redhat.com>