iio: accel: st_accel: Drop unnecessary #else branch for ACPI

ACPI_PTR() takes care of the argument in case of !CONFIG_ACPI.
Remove unnecessary #else branch.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>