staging: comedi: pcmuio: remove subdevice private data

The subdevice private data is only needed for each 'asic' not for each
subdevice. Since the 'asic' can be calculated easily from the subdevice
we can merge the subdevice private data members directly into the
private data.

This removes the need to kcalloc/free the subdevice private data and
saves a bit of space.
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>