drm/tegra: Fix window[0] base address corruption

Window uses shared stride for UV planes and tegra_dc_window struct
defines array of 2 strides per window. That's not taken in account
during setting up of the window addresses and strides, resulting in
out-of-bounds write of the 3-rd (non-existent) V plane stride that
overwrites Y plane base address.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
[treding@nvidia.com: explain why the V-plane stride is ignored]
Signed-off-by: Thierry Reding <treding@nvidia.com>