drm/msm/mdp5: Fix mdp5_init error path for failed mdp5_kms allocation

When allocation for mdp5_kms fails, calling mdp5_destroy() leads to undefined
behaviour, likely a nullptr exception or use-after-free troubles.
Signed-off-by: Roy Spliet <nouveau@spliet.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/disp/mdp5/mdp5_kms.c

@@ -943,7 +943,8 @@ static int mdp5_init(struct platform_device *pdev, struct drm_device *dev)
 
 	return 0;
 fail:
-	mdp5_destroy(pdev);
+	if (mdp5_kms)
+		mdp5_destroy(pdev);
 	return ret;
 }