virtio_ring: use helper function is_power_of_2()

Use helper function is_power_of_2() to check if num is power of two.
Minor readability improvement.

Signed-off-by: Shaoqin Huang <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>
Reviewed-by: Xuan Zhuo <[e-mail]>

drivers/virtio/virtio_ring.c

···
 	dma_addr_t dma_addr;
 
 	/* We assume num is a power of 2. */
-	if (num & (num - 1)) {
+	if (!is_power_of_2(num)) {
 		dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
 		return -EINVAL;
 	}