drm/tegra: debugfs cleanup cannot fail

The debugfs cleanup code never fails, so no error is returned. Therefore
the functions can all return void instead.

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

diff --cc drivers/gpu/drm/tegra/dsi.c
Simple merge

diff --cc drivers/gpu/drm/tegra/hdmi.c
Simple merge

diff --cc drivers/gpu/drm/tegra/sor.c
Simple merge