staging: comedi: das800: tidy up das800_di_insn_bits()

For digital input subdevices, the (*insn_bits) function simply needs
to return the status of the input channels in data[1].

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>