ARM: dts: socfpga: Remove unit name for LEDs in EBV SOCrates

GPIO LEDs in the Cyclone5 EBV SOCrates board have a unit name but no reg
property. Indeed, GPIO LEDs do not need such a property. They do not
need a unit name neither. This will trigger the following warnings when
compiled with W=1:

Node /gpio-leds/led@0 has a unit name, but no reg property
Node /gpio-leds/led@1 has a unit name, but no reg property
Node /gpio-leds/led@2 has a unit name, but no reg property

The solution is to remove the unit name. In order to have unique node
names, a rename is necessary. This should be harmless as all the LEDs
have a 'label' property, hence their name do not derive from the node
name and will stay the same after this patch.

Signed-off-by: Florian Vaussard <florian.vaussard@heig-vd.ch>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>