drm: add idr_init to drm_stub.c

Brown paper bag for me this patch chunk didn't make it in the first application
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/drm_stub.c

@@ -72,6 +72,8 @@ static int drm_fill_in_dev(struct drm_device * dev, struct pci_dev *pdev,
 	mutex_init(&dev->struct_mutex);
 	mutex_init(&dev->ctxlist_mutex);
 
+	idr_init(&dev->drw_idr);
+
 	dev->pdev = pdev;
 	dev->pci_device = pdev->device;
 	dev->pci_vendor = pdev->vendor;