staging: comedi: multiq3: allow user to reset encoder channels

Currently this driver resets all the encoder channels when the driver
is first attached. Add a (*insn_config) to the subdevice to allow the
use to reset the channels manually.

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