staging: comedi: quatech_daqp_cs: use (*insn_bits) for digital outputs

Change the subdevice operation used to write the digital outputs from
a (*insn_write) to a (*insn_bits) function. The (*insn_write) functions
are expected to write 'insn->n' number of samples. The (*insn_bits)
functions just write a single sample (insn->n = 1). Change the return
from '1' to 'insn->n' to clarify what the return is.

Using an (*insn_bits) function to write the digital outputs also allows
the user to read the current state of the output channels.

Fix the io operation used to update the digital outputs. The register is
only 8-bits and should by updated with an outb() not an outw().

Also, set the 'maxdata' for the subdevice. For digital io this value
should be '1' (digital io can only be 1 or 0).

Remove the setting of the len_chanlist for the subdevice. This variable
only has meaning for subdevices that support asynchronous commands. The
comedi core will initialize it appropriately during the postconfig.

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>