iio: accel: bma220: Mark PM functions as __maybe_unused

Instead of using ugly ifdeffery, mark PM functions as __maybe_unused.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200831090813.78841-4-andriy.shevchenko@linux.intel.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>