leds-qpnp: reduce WLED max brightness to 255, as dictated by led-class

Signed-off-by: Courtney Cavin <courtney.cavin@sonymobile.com>
Merge pull request #10 from andersson/for-alin/qpnp-leds-max-brightness

leds-qpnp: reduce WLED max brightness to 255, as dictated by led-class