iio: dac: mcp4922: drop remove() callback

By using devm_iio_device_register(), we can drop the remove() callback
in the mcp4922 driver. We can also remove spi_set_drvdata() since there
are no more callers of spi_get_drvdata(). Also use dev_err_probe()
while we are at it.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20240712-iio-regulator-refactor-round-3-v1-4-835017bae43d@baylibre.com


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