drm/tegra: Fix planar formats on Tegra186 and later

Use the correct pitch when programming the DC_WIN_PLANAR_STORAGE_UV
register's PITCH_U field to ensure the correct value is used in all
cases. This isn't currently causing any problems because the pitch
for both U and V planes is always the same.

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