f2fs: fix to correct check conditions in f2fs_cross_rename

Should be "old_dir" here.

Fixes: 5c57132e ("f2fs: support project quota")
Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>