ARM: dts: imx: Cleanup style around assignment operator

Use a space before and after assignment operator to have consistent
style.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>