doc: fix names of *SOURCE constants to *_SRC
doc: fix names of *SOURCE constants to *_SRC

Synchronises the content of the documentation with the actually content of the include files.

olsonse/comedilib,olsonse/comedilib,Linux-Comedi/comedilib,olsonse/comedilib,olsonse/comedilib,Linux-Comedi/comedilib,Linux-Comedi/comedilib,Linux-Comedi/comedilib,olsonse/comedilib,Linux-Comedi/comedilib,Linux-Comedi/comedilib,olsonse/comedilib