renderer: fix a leak in resource attach

Just return if the resource has been attached a iov
to avoid memory leak.

Signed-off-by: Li Qiang <liq3ea@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/vrend_renderer.c

@@ -4031,6 +4031,9 @@ int vrend_renderer_resource_attach_iov(int res_handle, struct iovec *iov,
    if (!res)
       return EINVAL;
 
+   if (res->iov)
+      return 0;
+
    /* work out size and max resource size */
    res->iov = iov;
    res->num_iovs = num_iovs;