ARM: dts: imx: Fix incorrect display nodes notation

The following build warnings are seen with W=1:

Warning (unit_address_vs_reg): Node /display@di0 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /display@di1 has a unit name, but no reg property

Fix all these warnings by changing 'display@diX' to 'dispX'.

Signed-off-by: Marco Franchi <marco.franchi@nxp.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>