udf: change maintainer

I've tried to contact Ben Fennema a few times but without success.  Since I'm
currently probably closest to being an UDF maintainer, I guess it's fine to
also change the entry in MAINTAINERS.

Signed-off-by: Jan Kara <jack@suse.cz>
Cc: <bfennema@falcon.csc.calpoly.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>