arm64: dts: mediatek: mt8186: Fix systimer 13 MHz clock description

The systimer block derives its 13 MHz clock by dividing the main 26 MHz
oscillator clock by 2 internally. The 13 MHz clock is not a separate
oscillator.

Fix this by making the 13 MHz clock a divide-by-2 fixed factor clock,
taking its input from the main 26 MHz oscillator.

Fixes: 2e78620b ("arm64: dts: Add MediaTek MT8186 dts and evaluation board and Makefile")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221201084229.3464449-5-wenst@chromium.orgSigned-off-by: Matthias Brugger <matthias.bgg@gmail.com>

arch/arm64/boot/dts/mediatek/mt8186.dtsi

@@ -215,10 +215,12 @@ l3_0: l3-cache {
 		};
 	};
 
-	clk13m: oscillator-13m {
-		compatible = "fixed-clock";
+	clk13m: fixed-factor-clock-13m {
+		compatible = "fixed-factor-clock";
 		#clock-cells = <0>;
-		clock-frequency = <13000000>;
+		clocks = <&clk26m>;
+		clock-div = <2>;
+		clock-mult = <1>;
 		clock-output-names = "clk13m";
 	};