staging: comedi: pcmuio: fix pcmuio_dio_insn_bits()

This dio subdevice (*insn_bits) function does not follow the "norm"
for comedi drivers. It also _appears_ to return the incorrect state
of the channels.

Use the comedi_dio_update_state() helper to handle the boilerplate
for updating the output channel state. Due to the hardware we then
need to invert the state and mask the input channels before updating
the outputs.

Then read the hardware and invert the result to get the current true
state of the dio channels.

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>