arm64: dts: imx8mm-emcon: Fix the regulator names

Fix the regulator names as per rohm,bd71847-pmic.yaml to fix the
following schema warnings:

imx8mm-emcon-avari.dtb: pmic@4b: regulators:LDO1:regulator-name:0: 'LDO1' does not match '^ldo[1-6]$'

Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>