arm64: dts: marvell: cn9131-db: drop unneeded flash address/size-cells

arm64: dts: marvell: cn9131-db: drop unneeded flash address/size-cells

Flash node uses single "partition" node to describe partitions, so
remove deprecated address/size-cells properties to also fix dtc W=1
warnings:

  cn9131-db.dtsi:140.10-163.4: Warning (avoid_unnecessary_addr_size): /cp1/config-space@f4000000/spi@700680/flash@0: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>