ARM: zynq: Fix leds subnode name for zc702/zybo-z7

Fix the leds subnode names to match (^led-[0-9a-f]$|led).

Similar change has been also done by commit 9a19a39e ("arm64: dts:
zynqmp: Fix leds subnode name for zcu100/ultra96 v1").

The patch is fixing these warnings:
.../zynq-zc702.dt.yaml: leds: 'ds23' does not match any of the regexes:
'(^led-[0-9a-f]$|led)', 'pinctrl-[0-9]+'
>From schema: .../Documentation/devicetree/bindings/leds/leds-gpio.yaml
.../zynq-zybo-z7.dt.yaml: gpio-leds: 'ld4' does not match any of the
regexes: '(^led-[0-9a-f]$|led)', 'pinctrl-[0-9]+'
>From schema: .../Documentation/devicetree/bindings/leds/leds-gpio.yaml

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/607a66783b129294364abf09a6fc8abd241ff4ee.1606397101.git.michal.simek@xilinx.com