docs: dt: writing-bindings: Update URL to DT schemas

The previous URL was giving a 404 error.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220627223950.35748-1-paul@crapouillou.net

Documentation/devicetree/bindings/writing-bindings.rst

@@ -53,7 +53,7 @@ Properties
 
 - DO use common property unit suffixes for properties with scientific units.
   Recommended suffixes are listed at
-  https://github.com/devicetree-org/dt-schema/blob/master/schemas/property-units.yaml
+  https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml
 
 - DO define properties in terms of constraints. How many entries? What are
   possible values? What is the order?