orangefs: clean up debugfs

We recently refactored the Orangefs debugfs code.
The refactor seemed to trigger dan.carpenter@oracle.com's
static tester to find a possible double-free in the code.

While designing the fix we saw a condition under which the
buffer being freed could also be overflowed.

We also realized how to rebuild the related debugfs file's
"contents" (a string) without deleting and re-creating the file.

This fix should eliminate the possible double-free, the
potential overflow and improve code readability.

Signed-off-by: Mike Marshall <hubcap@omnibond.com>
Signed-off-by: Martin Brandenburg <martin@omnibond.com>