arm64: tegra: Fix Tegra186 SOR supply

The following warning is observed on the Jetson TX2 platform ...

 WARNING KERN tegra-sor 15540000.sor: 15540000.sor supply \
              vdd-hdmi-dp-pll not found, using dummy regulator

The problem is caused because the regulator for the SOR device is
missing the '-supply' suffix in Device-Tree. Therefore, add the
'-supply' suffix to fix this warning.

Fixes: 3fdfaf87 ("arm64: tegra: Enable DP support on Jetson TX2")
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>