staging: comedi: ni_stc.h: tidy up AI_Output_Control_Register and bits

staging: comedi: ni_stc.h: tidy up AI_Output_Control_Register and bits

Rename the CamelCase. Use the BIT() macro to define the bits.

Tidy up the programming of this register un ni_ai_reset() by using a
local variable to set the common bits then writing the register in the
common code path.

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>