virtio: Add module.h to drivers/virtio users.

Up to now, the module.h header was as hard to keep out as
sunlight.  But we are cleaning that up.  Fix the virtio users
who simply expect module.h to be there in every C file.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

drivers/virtio/virtio.c

 #include <linux/virtio.h>
 #include <linux/spinlock.h>
 #include <linux/virtio_config.h>
+#include <linux/module.h>
 
 /* Unique numbering for virtio devices. */
 static unsigned int dev_index;

drivers/virtio/virtio_balloon.c

@@ -25,6 +25,7 @@
 #include <linux/freezer.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
+#include <linux/module.h>
 
 struct virtio_balloon
 {

drivers/virtio/virtio_ring.c

@@ -21,6 +21,7 @@
 #include <linux/virtio_config.h>
 #include <linux/device.h>
 #include <linux/slab.h>
+#include <linux/module.h>
 
 /* virtio guest is communicating with a virtual "device" that actually runs on
  * a host processor.  Memory barriers are used to control SMP effects. */