staging: comedi: pcmmio: there is only one asic

The board supported by this driver only has one WinSystems WS16C48 asic
on it that handles the digital i/o.

Remove the 'asics' struct array in the private data and add members for
the single 'asic_iobase' and the spinlock used by the asic.

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>