iio: adc: ad7173: Remove index from temp channel

Temperature channel is unique per device, index is not needed.
This is breaking userspace: Include fixes tag to be released within the
same rc cycle.

Fixes: 76a1e6a4

 ("iio: adc: ad7173: add AD7173 driver")
Signed-off-by: Dumitru Ceclan <dumitru.ceclan@analog.com>
Link: https://lore.kernel.org/r/20240521-ad7173-fixes-v1-3-8161cc7f3ad1@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>