staging: comedi: addi_apci_3xxx: fix digital input 'insn_bits' function

This driver does not follow the comedi API. The digital input 'insn_bits'
function is supposed to return the status of all the input channels in
data[1]. Currently this function is returning the status in data[0]. It
is also unnecessarily testing the size of the return buffer.

Fix the function so it works like the comedi core expects. The core can
then use the function to emulate the 'insn_read' function for individual
channels. This allows removing the i_APCI3XXX_InsnReadDigitalInput()
function.

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>