ARM: dts: sunplus: sp7021: drop incorrect spi-max-frequency

spi-max-frequency is a property of a SPI slave device, not controller:

sunplus-sp7021-demo-v3.dtb: spi@f480: Unevaluated properties are not allowed ('spi-max-frequency' was unexpected)

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

arch/arm/boot/dts/sunplus-sp7021.dtsi

···
 			interrupt-names = "dma_w", "master_risc", "slave_risc";
 			clocks = <&clkc CLK_SPI_COMBO_1>;
 			resets = <&rstc RST_SPI_COMBO_1>;
-			spi-max-frequency = <25000000>;
 			status = "disabled";
 		};
 
···
 			interrupt-names = "dma_w", "master_risc", "slave_risc";
 			clocks = <&clkc CLK_SPI_COMBO_2>;
 			resets = <&rstc RST_SPI_COMBO_2>;
-			spi-max-frequency = <25000000>;
 			status = "disabled";
 		};
 
···
 			interrupt-names = "dma_w", "master_risc", "slave_risc";
 			clocks = <&clkc CLK_SPI_COMBO_3>;
 			resets = <&rstc RST_SPI_COMBO_3>;
-			spi-max-frequency = <25000000>;
 			status = "disabled";
 		};