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

Signed-off-by: Courtney Cavin <courtney.cavin@sonymobile.com>
Signed-off-by: Chirayu Desai <chirayudesai1@gmail.com>
Change-Id: I1e6306590ba77a43fc0189fd737794dadf126699