iio: Comment that the LSM303D also has the Magnetometer DRDY

Per its datasheet, the LSM303D also features that pin.

Signed-off-by: Marius Hoch <mail@mariushoch.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Hans de Goede <hansg@kernel.org>
Link: https://lore.kernel.org/r/20230415231130.115094-6-mail@mariushoch.de


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