drm/tegra: hub: Remove bogus connection mutex check

The Tegra DRM never actually took that lock, so the driver was broken
until generic locking was added in commit:

commit b962a12050a387e4bbf3a48745afe1d29d396b0d
Author: Rob Clark <[e-mail]>
Date: Mon Oct 22 14:31:22 2018 +0200

drm/atomic: integrate modeset lock with private objects

It's now no longer necessary to take that lock, so drop the check.

v2: add rationale for why it is now safe to drop the check (Daniel)

Reviewed-by: Daniel Vetter <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

drivers/gpu/drm/tegra/hub.c

···
 tegra_display_hub_get_state(struct tegra_display_hub *hub,
 			    struct drm_atomic_state *state)
 {
-	struct drm_device *drm = dev_get_drvdata(hub->client.parent);
 	struct drm_private_state *priv;
-
-	WARN_ON(!drm_modeset_is_locked(&drm->mode_config.connection_mutex));
 
 	priv = drm_atomic_get_private_obj_state(state, &hub->base);
 	if (IS_ERR(priv))