ARM: dts: mvebu: Update comment for main PLL frequency

The actual frequency was updated in commit ae142bd9 ("ARM: mvebu:
Fix the main PLL frequency on Armada 375, 38x and 39x SoCs") but the
comment was not updated. Update it now.
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>

arch/arm/boot/dts/armada-375.dtsi

@@ -65,7 +65,7 @@ aliases {
 	};
 
 	clocks {
-		/* 2 GHz fixed main PLL */
+		/* 1 GHz fixed main PLL */
 		mainpll: mainpll {
 			compatible = "fixed-clock";
 			#clock-cells = <0>;

arch/arm/boot/dts/armada-38x.dtsi

@@ -661,7 +661,7 @@ spi1: spi@10680 {
 	};
 
 	clocks {
-		/* 2 GHz fixed main PLL */
+		/* 1 GHz fixed main PLL */
 		mainpll: mainpll {
 			compatible = "fixed-clock";
 			#clock-cells = <0>;

arch/arm/boot/dts/armada-39x.dtsi

@@ -573,7 +573,7 @@ spi1: spi@10680 {
 	};
 
 	clocks {
-		/* 2 GHz fixed main PLL */
+		/* 1 GHz fixed main PLL */
 		mainpll: mainpll {
 			compatible = "fixed-clock";
 			#clock-cells = <0>;