Staging: comedi: kcomedilib: delete dio.c and get.c

Merge these two files into kcomedilib_main.c as they are tiny.

This will also let us get rid of another global symbol in the future.

Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>