drm/tegra: Handle drm_atomic_helper_swap_state failure

drm_atomic_helper_swap_state() will be changed to interruptible waiting
in the next few commits, so all drivers have to be changed to handling
failure.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Jonathan Hunter <jonathanh@nvidia.com>
Cc: linux-tegra@vger.kernel.org
Link: http://patchwork.freedesktop.org/patch/msgid/20170711143314.2148-9-maarten.lankhorst@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/tegra/drm.c

@@ -100,7 +100,12 @@ static int tegra_atomic_commit(struct drm_device *drm,
 	 * the software side now.
 	 */
 
-	drm_atomic_helper_swap_state(state, true);
+	err = drm_atomic_helper_swap_state(state, true);
+	if (err) {
+		mutex_unlock(&tegra->commit.lock);
+		drm_atomic_helper_cleanup_planes(drm, state);
+		return err;
+	}
 
 	drm_atomic_state_get(state);
 	if (nonblock)