riscv: dts: microchip: remove spi-max-frequency property

spi-max-frequency property is supposed to be a per SPI peripheral device
property, not a SPI controller property, so remove it.
Reported-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/lkml/20220526014141.2872567-1-robh@kernel.org/Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

arch/riscv/boot/dts/microchip/mpfs.dtsi

@@ -290,7 +290,6 @@ spi1: spi@20109000 {
 			interrupt-parent = <&plic>;
 			interrupts = <55>;
 			clocks = <&clkcfg CLK_SPI1>;
-			spi-max-frequency = <25000000>;
 			status = "disabled";
 		};
 
@@ -302,7 +301,6 @@ qspi: spi@21000000 {
 			interrupt-parent = <&plic>;
 			interrupts = <85>;
 			clocks = <&clkcfg CLK_QSPI>;
-			spi-max-frequency = <25000000>;
 			status = "disabled";
 		};