regulator: dt-bindings: pca9450: Make interrupt optional

The interrupt is optional in hardware and not connected on
some boards. Make it optional in the binding.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Link: https://patch.msgid.link/20240708084107.38986-3-frieder@fris.de


Signed-off-by: Mark Brown <broonie@kernel.org>