arm64: dts: hisilicon: hi3660: add dedicated hi3660-usb3-otg-bc compatible

Each syscon node must come with a dedicated/specific compatible, which
is also reported by dtbs_check:

hi3660-hikey960.dtb: usb3_otg_bc@ff200000: compatible: ['syscon', 'simple-mfd'] is too short

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Krzysztof Kozlowski <[e-mail]>

arch/arm64/boot/dts/hisilicon/hi3660.dtsi

···
 		};
 
 		usb3_otg_bc: usb3_otg_bc@ff200000 {
-			compatible = "syscon", "simple-mfd";
+			compatible = "hisilicon,hi3660-usb3-otg-bc", "syscon", "simple-mfd";
 			reg = <0x0 0xff200000 0x0 0x1000>;
 
 			usb_phy: usb-phy {