staging: comedi: addi_apci_1500: 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 returns the status in data[0].

Fix the function so it works like the comedi core expects.

The 'insn_read' and 'insn_Write' functions for the digital input subdevice
cannot be removed yet. This driver is again abusing the API and uses these
functions to initialize the board and start/stop "events" generated by the
board. These will be addressed later.

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>