drm/omap: fix omap_fbdev_free() when omap_fbdev_create() wasn't called

If we have no crtcs/connectors, fbdev init goes fine, but
omap_fbdev_create() is never called. This means that omap_fbdev->bo is
NULL and omap_fbdev_free() crashes.

Add a check to omap_fbdev_free() to handle the NULL case.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/gpu/drm/omapdrm/omap_fbdev.c

@@ -303,7 +303,8 @@ void omap_fbdev_free(struct drm_device *dev)
 	fbdev = to_omap_fbdev(priv->fbdev);
 
 	/* unpin the GEM object pinned in omap_fbdev_create() */
-	omap_gem_unpin(fbdev->bo);
+	if (fbdev->bo)
+		omap_gem_unpin(fbdev->bo);
 
 	/* this will free the backing object */
 	if (fbdev->fb)