staging: comedi: vmk80xx: use comedi_dio_update_state()

Use comedi_dio_update_state() to handle the boilerplate code to update
the subdevice s->state.

Tidy up the vmk80xx_do_insn_bits() function a bit.

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>