staging:iio:adc:ad7606 refactor to remove st->irq and st->id.

id wasn't used anywhere and st->irq can be removed by simply
passing it into the core remove function (trivially available in
the two bus implementations).

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>