arm64: dts: imx8mn: Update VDD_ARM 1.2GHz setpoint voltage

The latest datasheet Rev. 0.1, 03/2020 removes below constrain:

"If VDD_SOC/GPU/DDR = 0.95V, then VDD_ARM must be >= 0.95V."

So, for 1.2GHz setpoint VDD_ARM can use its typical voltage
directly.

The datasheet can be downloaded from below link:
https://www.nxp.com/docs/en/data-sheet/IMX8MNCEC.pdfSigned-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mn.dtsi

@@ -121,7 +121,7 @@ a53_opp_table: opp-table {
 
 		opp-1200000000 {
 			opp-hz = /bits/ 64 <1200000000>;
-			opp-microvolt = <950000>;
+			opp-microvolt = <850000>;
 			opp-supported-hw = <0xb00>, <0x7>;
 			clock-latency-ns = <150000>;
 			opp-suspend;