ARM: dts: imx6dl-yapp4: Remove the unused white LED channel

Since the reg property was added to each channel node in commit
b86d3d21 ("ARM: dts: imx6dl-yapp4: Add reg property to the lp5562
channel node") it is possible to skip unused channels.

Remove the actually unused white LED channel.

Signed-off-by: Michal Vokáč <michal.vokac@ysoft.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>