drm/nouveau/i2c: drop parent refcount when creating ports

Fixes issue where i2c subdev never gets destroyed due to its subobjects
holding references.  This will mean the i2c subdev refcount goes
negative during its destruction, but this isn't an issue in practice.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/core/subdev/i2c/base.c

@@ -142,6 +142,7 @@ nouveau_i2c_port_create_(struct nouveau_object *parent,
 	/* drop port's i2c subdev refcount, i2c handles this itself */
 	if (ret == 0) {
 		list_add_tail(&port->head, &i2c->ports);
+		atomic_dec(&parent->refcount);
 		atomic_dec(&engine->refcount);
 	}