[S390] sparse: fix sparse static warnings

Make functions and data static to avoid sparse warnings.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
index aec60d5..83c69fb 100644
--- a/drivers/s390/kvm/kvm_virtio.c
+++ b/drivers/s390/kvm/kvm_virtio.c
@@ -33,7 +33,7 @@
  * The pointer to our (page) of device descriptions.
  */
 static void *kvm_devices;
-struct work_struct hotplug_work;
+static struct work_struct hotplug_work;
 
 struct kvm_device {
 	struct virtio_device vdev;