iio: adc: cc10001: Add local struct device *dev variable to avoid repitition

There are lots of uses of this in probe() and we are about to introduce
some more, so add a local variable to simplify this.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20221016170950.387751-2-jic23@kernel.org