iio: adc: ad7173: Fix ! vs ~ typo in ad7173_sel_clk()

This was obviously supposed to be a bitwise negate instead of logical.

Fixes: 76a1e6a4 ("iio: adc: ad7173: add AD7173 driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/5401c681-c4aa-4fab-8c8c-8f0a379e2687@moroto.mountain


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