mfd: intel_soc_pmic_bxtwc: Drop redundant ACPI_PTR()

The driver depends on ACPI (via MFD_INTEL_PMC_BXT), ACPI_PTR() resolution
is always the same. Otherwise a compiler may produce a warning.

That said, the rule of thumb either ugly ifdeffery with ACPI_PTR or
none should be used in a driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220628221747.33956-7-andriy.shevchenko@linux.intel.com