ARM: dts: bcm-cygnus: Update spi clock properties

PL022 binding require two clocks to be defined but broadcom cygnus
platform doesn't comply with bindings and define only one clock.

Update spi clocks and clocks-names property by adding appropriate clock
reference to make it compliant with bindings.

CC: Florian Fainelli <[e-mail]>
Signed-off-by: Kuldeep Singh <[e-mail]>
Signed-off-by: Florian Fainelli <[e-mail]>

arch/arm/boot/dts/bcm-cygnus.dtsi

···
 			#size-cells = <0>;
 			interrupts = <GIC_SPI 78 IRQ_TYPE_LEVEL_HIGH>;
 			pinctrl-0 = <&spi_0>;
-			clocks = <&axi81_clk>;
-			clock-names = "apb_pclk";
+			clocks = <&axi81_clk>, <&axi81_clk>;
+			clock-names = "sspclk", "apb_pclk";
 			status = "disabled";
 		};
 
···
 			#size-cells = <0>;
 			interrupts = <GIC_SPI 79 IRQ_TYPE_LEVEL_HIGH>;
 			pinctrl-0 = <&spi_1>;
-			clocks = <&axi81_clk>;
-			clock-names = "apb_pclk";
+			clocks = <&axi81_clk>, <&axi81_clk>;
+			clock-names = "sspclk", "apb_pclk";
 			status = "disabled";
 		};
 
···
 			#size-cells = <0>;
 			interrupts = <GIC_SPI 80 IRQ_TYPE_LEVEL_HIGH>;
 			pinctrl-0 = <&spi_2>;
-			clocks = <&axi81_clk>;
-			clock-names = "apb_pclk";
+			clocks = <&axi81_clk>, <&axi81_clk>;
+			clock-names = "sspclk", "apb_pclk";
 			status = "disabled";
 		};