dt-bindings: serial: 8250: correct Nuvoton NPCM850 compatible

Nuvoton NPCM850 UART is compatible with NPCM750, so add proper fallback
to match existing DTS and Linux driver.

Fixes: c8177f90 ("dt-bindings: serial: 8250: Add npcm845 compatible string")
Signed-off-by: NKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: NRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230124091602.44027-3-krzysztof.kozlowski@linaro.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/8250.yaml

@@ -62,7 +62,6 @@ properties:
       - const: mrvl,pxa-uart
       - const: nuvoton,wpcm450-uart
       - const: nuvoton,npcm750-uart
-      - const: nuvoton,npcm845-uart
       - const: nvidia,tegra20-uart
       - const: nxp,lpc3220-uart
       - items:
@@ -92,6 +91,10 @@ properties:
           - enum:
               - ns16550 # Deprecated, unless the FIFO really is broken
               - ns16550a
+      - items:
+          - enum:
+              - nuvoton,npcm845-uart
+          - const: nuvoton,npcm750-uart
       - items:
           - enum:
               - ralink,mt7620a-uart