iio: sx9310: Use regmap_read_poll_timeout() for compensation

Simplify compensation stage by using regmap_read_poll_timeout().

Signed-off-by: Daniel Campello <campello@chromium.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>