staging: comedi: addi_apci_3120: tidy up analog input subdevice init

For aesthetics, add some white space to the analog input subdevice
initialization.

The async command support in this driver is pretty messed up. I'm not
really sure if it actually works yet. Luckly this driver was not
setting the SDF_CMD_READ subdev_flag so the command support was not
actually getting enabled.

The command support only works if an interrupt is available. Refactor
the subdevice init so that the command support is only hooked up if
we have an interrupt. For now always disable the command support. Once
the driver has been cleaned up the command will be enabled.

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>