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_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
 {