iio: humidity: hts211: Factor out everything under direct mode claim into helper...

iio: humidity: hts211: Factor out everything under direct mode claim into helper functions.

Pulling out the functionality of read_raw() and write_raw() callbacks
so that only the mode claim is done in the initial call allows for
direct returns and simpler error handling in the new __hts211_write_raw()
/ __hts211_read_raw() functions.

Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com>
Link: https://patch.msgid.link/20250331121317.1694135-14-jic23@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>