ubifs: Fix directory size calculation for symlinks

commit 00ee8b60102862f4daf0814d12a2ea2744fc0b9b upstream

We have to account the name of the symlink and not the target length.

Fixes: ca7f85be ("ubifs: Add support for encrypted symlinks")
Cc: <stable@vger.kernel.org>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>