As the 'reg' property is mandatory in the subnodes, improve the
example by adding the unit address to the sysled node.

This prevents the following build warning with W=1:

Node /soc/aips@70000000/spba@70000000/ecspi@70010000/pmic@0/leds/sysled0 has a reg or ranges property, but no unit name
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>