staging: comedi: ni_mio_common: tidy up the gpct counter subdevice init

For aesthetics, add some whitespace to the subdevice init and
tidy it up a bit.

Unfortunately we can't get rid of the '#ifdef PCIDMA' here yet due
to other ifdefery in this file. For now just add the correct test
so that the async command support is not hooked up unless we have
an IRQ and DMA.

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>