regulator: maxim,max8973: Document interrupts property

One of the examples in the bindings has an interrupts property and the
Linux kernel driver has support for requesting an interrupt as well. It
looks like the absence from the bindings was just an oversight. Add the
property to make sure the examples can be validated.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20211206153432.226963-1-thierry.reding@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/maxim,max8973.yaml

@@ -86,6 +86,9 @@ properties:
   reg:
     maxItems: 1
 
+  interrupts:
+    maxItems: 1
+
 required:
   - compatible
   - reg