virtio_blk: Add missing 'static' qualifiers

Add missing 'static' qualifiers
Signed-off-by: Jonghwan Choi <jhbird.choi@samsung.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/block/virtio_blk.c

@@ -20,7 +20,7 @@ module_param(use_bio, bool, S_IRUGO);
 static int major;
 static DEFINE_IDA(vd_index_ida);
 
-struct workqueue_struct *virtblk_wq;
+static struct workqueue_struct *virtblk_wq;
 
 struct virtio_blk
 {