The VCC supply property is not populated for the temperature sensor on
the P2888 board and so the following warning is observed on boot ...

 lm90 0-004c: 0-004c supply vcc not found, using dummy regulator

On the P2888 board, the VCC supply for the temperature sensor is
connected to the 'vdd_1v8ls' rail. Add the 'vcc-supply' property for
the temperature sensor to prevent this warning message from occurring.

Fixes: 8b457812 ('arm64: tegra: Add temperature sensor on P2888')
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>