drm/msm: set priv->kms to NULL before uninit

otherwise, priv->kms is non-NULL and msm_drm_uninit will cause a panic.
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/msm_drv.c

@@ -524,6 +524,7 @@ static int msm_drm_init(struct device *dev, struct drm_driver *drv)
 		 */
 		DRM_DEV_ERROR(dev, "failed to load kms\n");
 		ret = PTR_ERR(kms);
+		priv->kms = NULL;
 		goto err_msm_uninit;
 	}