staging: comedi: ni_stc.h: tidy up NI_M_AI_CFG_BYPASS_FIFO_REG bits

Rename the CamelCase and convert the enum into defines. Use the BIT()
macro to define the bits. Convert the inline helper functions into
macros.

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>