drm/tegra: Use correct relocation target offsets

When copying a relocation from userspace, copy the correct target
offset.

Signed-off-by: David Ung <davidu@nvidia.com>
Fixes: 961e3bea ("drm/tegra: Make job submission 64-bit safe")
Cc: stable@vger.kernel.org
[treding@nvidia.com: provide a better commit message]
Signed-off-by: Thierry Reding <treding@nvidia.com>