ARM: dts: rza2mevb: Fix LED node names

"make dtbs_check":

    arch/arm/boot/dts/r7s9210-rza2mevb.dtb: leds: 'green', 'red' do not match any of the regexes: '(^led-[0-9a-f]$|led)', 'pinctrl-[0-9]+'
	    From schema: Documentation/devicetree/bindings/leds/leds-gpio.yaml

Fix this by prefixing the LED node names with "led-".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/f6e2883c16803b5d90a26c38d8e61ad15096089c.1655301593.git.geert+renesas@glider.be