drm/tegra: Fixes for v5.6-rc1

These are a couple of quick fixes for regressions that were found during
the first two weeks of the merge window.
Signed-off-by: Dave Airlie <airlied@redhat.com>

From: Thierry Reding <thierry.reding@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200206172753.2185390-1-thierry.reding@gmail.com