iio: accel: bma220: Use dev_get_drvdata() directly

Instead of using to_spi_dev() + spi_get_drvdata(),
use dev_get_drvdata() to make code simpler.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200831090813.78841-3-andriy.shevchenko@linux.intel.com


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