virtio-mem: Assign boolean values to a bool variable

Fix the following coccicheck warnings:

./drivers/virtio/virtio_mem.c:2580:2-25: WARNING: Assignment
of 0/1 to bool variable.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Zhong <abaci-bugfix@linux.alibaba.com>
Link: https://lore.kernel.org/r/1611129031-82818-1-git-send-email-abaci-bugfix@linux.alibaba.com
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_mem.c

@@ -2577,7 +2577,7 @@ static int virtio_mem_probe(struct virtio_device *vdev)
 	 * actually in use (e.g., trying to reload the driver).
 	 */
 	if (vm->plugged_size) {
-		vm->unplug_all_required = 1;
+		vm->unplug_all_required = true;
 		dev_info(&vm->vdev->dev, "unplugging all memory is required\n");
 	}