staging: comedi: ni_stc.h: tidy up Write_Strobe_*_Register

The Write_Strobe_*_Register defines are noy used. Instead the more
descriptive Configuration_Memory_Clear, ADC_FIFO_Clear and DAC_FIFO_Clear
defines are used. Remove the unused defines and rename the CamelCase.

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>