Loongson3A7A: fix up serial clock freq to 50M.

Change-Id: Ib8f7bca49ffda252e2df7dc97e49d26cc9732cb9
Signed-off-by: QiaoChong <qiaochong@loongson.cn>

Targets/Bonito3a3000_7a/conf/Bonito3a3000_7a.dts

@@ -48,7 +48,7 @@
 			device_type = "serial";
 			compatible = "ns16550a";
 			reg = <0 0x10080000 0x100>;
-			clock-frequency = <125000000>;
+			clock-frequency = <50000000>;
 			interrupts = <72>;
 			interrupt-parent = <&platic>;
 			no-loopback-test;
@@ -58,7 +58,7 @@
 			device_type = "serial";
 			compatible = "ns16550a";
 			reg = <0 0x10080100 0x100>;
-			clock-frequency = <125000000>;
+			clock-frequency = <50000000>;
 			interrupts = <72>;
 			interrupt-parent = <&platic>;
 			no-loopback-test;
@@ -68,7 +68,7 @@
 			device_type = "serial";
 			compatible = "ns16550a";
 			reg = <0 0x10080200 0x100>;
-			clock-frequency = <125000000>;
+			clock-frequency = <50000000>;
 			interrupts = <72>;
 			interrupt-parent = <&platic>;
 			no-loopback-test;
@@ -78,7 +78,7 @@
 			device_type = "serial";
 			compatible = "ns16550a";
 			reg = <0 0x10080300 0x100>;
-			clock-frequency = <125000000>;
+			clock-frequency = <50000000>;
 			interrupts = <72>;
 			interrupt-parent = <&platic>;
 			no-loopback-test;