arm64: dts: hikey960: change bluetooth uart max-speed to 3mbps

Update bluetooth UART max-speed to 3Mbps
Signed-off-by: Guodong Xu <guodong.xu@linaro.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>

arch/arm64/boot/dts/hisilicon/hi3660-hikey960.dts

@@ -230,7 +230,7 @@ &uart4 {
 	bluetooth {
 		compatible = "ti,wl1837-st";
 		enable-gpios = <&gpio15 6 GPIO_ACTIVE_HIGH>;
-		max-speed = <921600>;
+		max-speed = <3000000>;
 	};
 };