mfd: Use dev_fwnode() instead of of_fwnode_handle()

mfd: Use dev_fwnode() instead of of_fwnode_handle()

irq_domain_create_simple() takes fwnode as the first argument. It can be
extracted from the struct device using dev_fwnode() helper instead of
using of_node with of_fwnode_handle().

So use the dev_fwnode() helper.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20250611104348.192092-13-jirislaby@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>