arm64: dts: imx: Pass a single BD71847 clock entry

Pass a single BD71847 clock entry to fix the following schema
warning:

imx8mm-var-som-symphony.dtb: pmic@4b: clocks: [[22], [0]] is too long
	from schema $id: http://devicetree.org/schemas/mfd/rohm,bd71847-pmic.yaml#



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