iio: adc: rtq6056: Use automated cleanup for mode handling in write_raw

iio: adc: rtq6056: Use automated cleanup for mode handling in write_raw

Using iio_device_claim_direct_scoped() to automate mode claim and release
simplifies code flow and allows for straight-forward error handling with
direct returns on errors.

Signed-off-by: Gabriel Schwartz <gschwartz@usp.br>
Reviewed-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com>
Reviewed-by: ChiYuan Huang <cy_huang@richtek.com>
Link: https://lore.kernel.org/r/20240426200118.20900-1-gschwartz@usp.br
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>