ARM: dts: exynos: drop undocumented samsung,sata-freq property in Exynos5250

The samsung,sata-freq property is not used (and not documented by
generic AHCI platform bindings), so can be safely dropped.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210811083859.28234-2-krzysztof.kozlowski@canonical.com

arch/arm/boot/dts/exynos5250.dtsi

@@ -386,7 +386,6 @@ tmu: tmu@10060000 {
 
 		sata: sata@122f0000 {
 			compatible = "snps,dwc-ahci";
-			samsung,sata-freq = <66>;
 			reg = <0x122F0000 0x1ff>;
 			interrupts = <GIC_SPI 115 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&clock CLK_SATA>, <&clock CLK_SCLK_SATA>;