iio: proximity: sx_common: Don't use IIO device for properties

iio: proximity: sx_common: Don't use IIO device for properties

It's not correct to use artificial device created by IIO core to
retrieve device properties. Even ->get_default_reg() callback
takes a simple struct device pointer which suggests it wants to
operate on the real device.

Correct this by replacing pointer to IIO device by a real device
pointer in the caller of ->get_default_reg().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
Link: https://lore.kernel.org/r/20220615114746.2767-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>