arm64: tegra: Add reference clock to GM20B on Tegra210

This clock is required for the GPU to operate.
Signed-off-by: NAlexandre Courbot <acourbot@nvidia.com>
Signed-off-by: NThierry Reding <treding@nvidia.com>

arch/arm64/boot/dts/nvidia/tegra210.dtsi

@@ -226,8 +226,9 @@
 			     <GIC_SPI 158 IRQ_TYPE_LEVEL_HIGH>;
 		interrupt-names = "stall", "nonstall";
 		clocks = <&tegra_car TEGRA210_CLK_GPU>,
-			 <&tegra_car TEGRA210_CLK_PLL_P_OUT5>;
-		clock-names = "gpu", "pwr";
+			 <&tegra_car TEGRA210_CLK_PLL_P_OUT5>,
+			 <&tegra_car TEGRA210_CLK_PLL_G_REF>;
+		clock-names = "gpu", "pwr", "ref";
 		resets = <&tegra_car 184>;
 		reset-names = "gpu";
 		status = "disabled";