iio: adc: ad4130: Fix spelling mistake "diffreential" -> "differential"

There is a spelling mistake in an error message. Fix it.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20221104093148.167765-1-colin.i.king@gmail.com


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