mfd: core: Set fwnode for created devices

The logic for setting the of_node on devices created by mfd did not set
the fwnode pointer to match, which caused fwnode-based APIs to
malfunction on these devices since the fwnode pointer was null. Fix
this.
Signed-off-by: Robert Hancock <hancock@sedsystems.ca>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/mfd-core.c

@@ -179,6 +179,7 @@ static int mfd_add_device(struct device *parent, int id,
 		for_each_child_of_node(parent->of_node, np) {
 			if (of_device_is_compatible(np, cell->of_compatible)) {
 				pdev->dev.of_node = np;
+				pdev->dev.fwnode = &np->fwnode;
 				break;
 			}
 		}