ARM: dts: socfpga: Drop ad-hoc UART clock frequency encoding from DT

The UART clock frequency can be obtained from the clock framework by the
ns16550 driver, so drop this redundant DT node.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <chin.liang.see@intel.com>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Ley Foon Tan <ley.foon.tan@intel.com>

arch/arm/dts/socfpga_arria10_socdk.dtsi

@@ -154,7 +154,6 @@
 };
 
 &uart1 {
-	clock-frequency = <50000000>;
 	u-boot,dm-pre-reloc;
 	status = "okay";
 };