clk: tegra20/30: Explicitly set parent clock for Video Decoder

The VDE parent won't be changed automatically to PLLC if bootloader
didn't do that for us, hence let's explicitly set the parent for
consistency.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>