docs: iio: Correct a typo

There are two EP9312, one of them should be 9315

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Link: https://lore.kernel.org/r/20210119030320.2860870-1-siyanteng@loongson.cn
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
1 file changed