iio: magnetometer: yas530: Apply documentation and style fixes

This commit gathers several minor changes.

In the device examples, "Xiaomi" is too generic, specific devices should be
listed here. E.g. Xiaomi Redmi 2 seems to have YAS537 but it's not fully clear
if this applies to all its variants. Samsung Galaxy S7 is often quoted in
conjunction with YAS537.

Removed defines for device IDs of YAS537 and YAS539, they are not needed so far.

Signed-off-by: Jakob Hauser <jahau@rocketmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/300e394a76eb30fa031ecb69b594e9f9a70dac42.1660337264.git.jahau@rocketmail.com


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