staging: comedi: me_daq: cleanup me_dio_insn_bits()

This function only needs to update the output channel state when
the 'mask' (data[0]) indicates that the state is changing. It's
also supposed to return the state for all the input and output
channels in data[1].

This function appears to work correctly but it's coded quite
differently form the other comedi drivers. Rework the function so
it follows the normal form. Also, use a couple local variables
for the mmio addresses used to read/write the dio ports.

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>