UBIFS: rename dumping functions

This commit re-names all functions which dump something from "dbg_dump_*()" to
"ubifs_dump_*()". This is done for consistency with UBI and because this way it
will be more logical once we remove the debugging sompilation option.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>