staging: comedi: pcmmio: remove 'asic' member from subdevice private data

This member of the subdevice private data is always initialized to '0' by
the only subdevice that uses it. Since we only have one asic on the board
it's really not needed. Just remove it.

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>