staging: comedi: ni_labpc: introduce labpc_setup_cmd6_reg()

Introduce a helper function to set the COMMAND6_REG.

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>