ACPI: PMIC: Replace open coded be16_to_cpu()

It's easier to understand the nature of a data type when
it's written explicitly. With that, replace open coded
endianess conversion.

As a side effect it fixes the returned value of
intel_crc_pmic_update_aux() since ACPI PMIC core code
expects negative or zero and never uses positive one.

While at it, use macros from bits.h to reduce a room for mistake.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>