ARM: dts: imx6dl-yapp4: Fix lp5562 LED driver probe

Since the LED multicolor framework support was added in commit
92a81562 ("leds: lp55xx: Add multicolor framework support to lp55xx")
LEDs on this platform stopped working.

Author of the framework attempted to accommodate this DT to the
framework in commit b86d3d21 ("ARM: dts: imx6dl-yapp4: Add reg property
to the lp5562 channel node") but that is not sufficient. A color property
is now required even if the multicolor framework is not used, otherwise
the driver probe fails:

  lp5562: probe of 1-0030 failed with error -22

Add the color property to fix this.

Fixes: 92a81562

 ("leds: lp55xx: Add multicolor framework support to lp55xx")
Cc: <stable@vger.kernel.org>
Cc: linux-leds@vger.kernel.org
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>