added error check for mmap() call
added error check for mmap() call

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