drm/omap: clear omap_obj->paddr in omap_gem_put_paddr()

Clear omap_obj's paddr when unmapping the memory, so that it's easier to
catch bad use of the paddr.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/omap_gem.c

@@ -828,6 +828,7 @@ int omap_gem_put_paddr(struct drm_gem_object *obj)
 				dev_err(obj->dev->dev,
 					"could not release unmap: %d\n", ret);
 			}
+			omap_obj->paddr = 0;
 			omap_obj->block = NULL;
 		}
 	}