f2fs: fix potential corruption when moving a directory

commit d94772154e524b329a168678836745d2773a6e02 upstream.

F2FS has the same issue in ext4_rename causing crash revealed by
xfstests/generic/707.

See also commit 0813299c586b ("ext4: Fix possible corruption when moving a directory")

CC: stable@vger.kernel.org
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>