f2fs: fix incorrect error path handling in f2fs_move_rehashed_dirents

Fix two bugs in error path of f2fs_move_rehashed_dirents:
 - release dir's inode page if fail to call kmalloc
 - recover i_current_depth if fail to converting

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>