ARM: dts: Update echi-omap DT binding example usage

Remove non-compatible id from examples.

CC: Alan Stern <stern@rowland.harvard.edu>
CC: Nishant Menon <nm@ti.com>
CC: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>