staging: comedi: pcmad: tidy up pcmad_attach()

Remove the comment before the function, the options are documented at
the beginning of the file.

Remove the PCMAD_SIZE define. It's only used in the attach to specify
the io region size.

For aesthetic reasons, add some whitespace to the subdevice init and
reorder them a bit.

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