ARM: pxa: zeus: Constify the software node

ARM: pxa: zeus: Constify the software node

When device properties are supplied to the devices, in
reality a software fwnode that holds those properties is
created which is then assigned to the device. If the device
properties are constant the software node can also be
constant.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Daniel Mack <daniel@zonque.org>
Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Cc: Robert Jarzmik <robert.jarzmik@free.fr>
Link: https://lore.kernel.org/r/20210303152814.35070-4-heikki.krogerus@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>