staging: comedi: plx9080.h: rename some macros for consistency

Most of the macros in "plx9080.h" that define register values are
single-bits flags of the form `PLX_<REG>_<FLAG>`, or are constant,
multi-bit values of the form `PLX_<REG>_<FIELD>_<VAL>`, or are
non-constant, function-like macros of the form `PLX_<REG>_<FIELD>(x)`.
Some of the macros for constant, multi-bit values do not currently
fit the pattern, so rename them for consistency.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>