ARM: dts: omap3: overo: remove unneded unit names in display nodes

This patch fixes the following DTC warnings for omap3-overo-gallop43.dtb,
omap3-overo-chestnut43.dtb, omap3-overo-storm-chestnut43.dtb,
omap3-overo-palo43.dtb, and omap3-overo-storm-palo43.dtb:

"display@0 has a unit name, but no reg property"

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>