dt-bindings: spi: spi-mux: rename flash node

The recent conversion of the common MTD properties to YAML now mandates
a particular node name for SPI flash devices.
Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210517153946.9502-1-michael@walle.ccSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-mux.yaml

@@ -72,7 +72,7 @@ examples:
 
             mux-controls = <&mux>;
 
-            spi-flash@0 {
+            flash@0 {
                 compatible = "jedec,spi-nor";
                 reg = <0>;
                 #address-cells = <1>;