drm/tegra: sor: Use correct SOR index on Tegra210

drm/tegra: sor: Use correct SOR index on Tegra210

BugLink: https://bugs.launchpad.net/bugs/1858428
[ Upstream commit 24e64f86da40e68c5f58af08796110f147b12193 ]

The device tree bindings for the Tegra210 SOR don't require the
controller instance to be defined, since the instance can be derived
from the compatible string. The index is never used on Tegra210, so we
got away with it not getting set. However, subsequent patches will
change that, so make sure the proper index is used.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>