ARM: tegra: Use symbolic names for gr3d clocks

Commit 05849c93 (ARM: tegra30: convert
device tree files to use CLK defines) updated the Tegra30 device tree to
use symbolic clock names but forgot to update this node.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>