UBIFS: stop re-defining UBI operations

Now when we use UBIFS helpers for all the I/O, we can remove the horrible hack
of re-defining UBI I/O functions.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

diff --cc fs/ubifs/debug.c
Simple merge

diff --cc fs/ubifs/debug.h
Simple merge