arm64: dts: zynqmp: Fix leds subnode name for zcu100/ultra96 v1

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

Similar change has been also done by commit 08dc0e5d ("arm64: dts:
meson: fix leds subnodes name").

The patch is fixing this warning:
avnet-ultra96-rev1.dt.yaml: leds: 'ds2', 'ds3', 'ds4', 'ds5' do not match
any of the regexes: '(^led-[0-9a-f]$|led)', 'pinctrl-[0-9]+'

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/1a69c3fa0291f991ffcf113ea222c713ba4d4ff0.1598264917.git.michal.simek@xilinx.com