The code as currently implemented does not work on big endian systems,
so fix it up.

Fixes: a2c8f92b ("ACPI: CPPC: Implement support for SystemIO registers")
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Suggested-by: NDan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/linux-acpi/20220111092928.GA24968@kili/Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NHuang Rui <ray.huang@amd.com>