hwrng: virtio - Constify id_table[]

id_table[] is not modified and an be made const to allow the compiler to
put it in read-only memory.

Before:
   text    data     bss     dec     hex filename
   1746     192       8    1946     79a drivers/char/hw_random/virtio-rng.o

After:
   text    data     bss     dec     hex filename
   1762     176       8    1946     79a drivers/char/hw_random/virtio-rng.o
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/virtio-rng.c

@@ -195,7 +195,7 @@ static int virtrng_restore(struct virtio_device *vdev)
 }
 #endif
 
-static struct virtio_device_id id_table[] = {
+static const struct virtio_device_id id_table[] = {
 	{ VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 	{ 0 },
 };