doc: dt: Fix broken reference in gpio-leds documentation
doc: dt: Fix broken reference in gpio-leds documentation

The gpios property is described in Documentation/devicetree/gpio.txt, so
reference this document.

Signed-off-by: Tobias Klauser <9249c549618448e4c699e8032ba6c7f0d7fd4b7f@distanz.ch>
Signed-off-by: Rob Herring <aa00819e304141d872f2e4b1c4be422ea3abbfe1@calxeda.com>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs