staging: comedi: aio_aio12_8: move comedi_lrange definition

For aesthetics, move the comedi_lrange definition used in this driver
to the follow the norm in comedi drivers and rename the variable.

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>