virtio-rng: don't crash if virtqueue is broken.

A bad implementation of virtio might cause us to mark the virtqueue
broken: we'll dev_err() in that case, and the device is useless, but
let's not BUG().

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/char/hw_random/virtio-rng.c

@@ -47,8 +47,7 @@ static void register_buffer(u8 *buf, size_t size)
 	sg_init_one(&sg, buf, size);
 
 	/* There should always be room for one buffer. */
-	if (virtqueue_add_inbuf(vq, &sg, 1, buf, GFP_KERNEL) < 0)
-		BUG();
+	virtqueue_add_inbuf(vq, &sg, 1, buf, GFP_KERNEL);
 
 	virtqueue_kick(vq);
 }