staging: comedi: cb_pcidas: tidy up analog input subdevice init

staging: comedi: cb_pcidas: tidy up analog input subdevice init

For aesthetics, add some whitespace to the subdevice initialization
and rename the subdevice functions to follow the normal form in
comedi drivers.

Async command support uses interrupts. For clarity, make sure the
driver has an IRQ before initializing command support.

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>