dt-bindings: arm: rockchip: correct the model name for Radxa ROCK 3A

According to https://radxa.com/products/rock3/3a,
the name of this board should be "Radxa ROCK 3A".
Suggested-by: FUKAUMI Naoki <naoki@radxa.com>
Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20240419103019.992586-2-amadeus@jmu.edu.cnSigned-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -789,7 +789,7 @@ properties:
           - const: radxa,rock2-square
           - const: rockchip,rk3288
 
-      - description: Radxa ROCK3 Model A
+      - description: Radxa ROCK 3A
         items:
           - const: radxa,rock3a
           - const: rockchip,rk3568