irqdomain: remoteproc: Switch to of_fwnode_handle()

of_node_to_fwnode() is irqdomain's reimplementation of the "officially"
defined of_fwnode_handle(). The former is in the process of being
removed, so use the latter instead.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Bjorn Andersson <andersson@kernel.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: linux-remoteproc@vger.kernel.org
Link: https://lore.kernel.org/r/20250319092951.37667-10-jirislaby@kernel.org


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>