arm64: dts: imx8mm-ddr4-evk: Align pin configuration group names with schema

Device tree schema expects pin configuration groups to end with 'grp'
suffix, otherwise dtbs_check complain with a warning like:

    ... do not match any of the regexes: 'grp$', 'pinctrl-[0-9]+'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mn-ddr4-evk.dts

@@ -155,7 +155,7 @@ ldo6_reg: LDO6 {
 };
 
 &iomuxc {
-	pinctrl_pmic: pmicirq {
+	pinctrl_pmic: pmicirqgrp {
 		fsl,pins = <
 			MX8MN_IOMUXC_GPIO1_IO03_GPIO1_IO3	0x41
 		>;