staging: comedi: pcmmio: tidy up the ai subdevice init

Add some whitespace to the ai subdevice init and reorder it a bit
to follow the "norm" in comedi drivers.

Remove the init of s->len_chanlist. This member is only used with
subdevices that support async commands. The core will default the
value correctly..

The ai subdevice only uses the s->private member to pass the iobase
to the analog input registers. It's just a copy of the dev->iobase,
use that instead.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>