arm64: dts: imx8qxp-mek: Do not use underscore in node name

Underscores are not recommended to be used in node names, so change
the pinctrl IO expander node name.

This change also makes the pinctrl node names to follow the convention
used by other pinctrl group names.
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8qxp-mek.dts

@@ -216,7 +216,7 @@ IMX8QXP_ENET0_RGMII_RXD3_CONN_ENET0_RGMII_RXD3		0x06000020
 		>;
 	};
 
-	pinctrl_ioexp_rst: ioexp_rst_grp {
+	pinctrl_ioexp_rst: ioexprstgrp {
 		fsl,pins = <
 			IMX8QXP_SPI2_SDO_LSIO_GPIO1_IO01			0x06000021
 		>;