staging:iio:cdc:ad7150: Change timeout units to seconds and use core support

Now we have core support for timeouts related to adaptive events, let us
use it.  Note the units of that attribute are seconds, so we also need
to scale the cycles value by the period of each sample.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210314181511.531414-12-jic23@kernel.org