arm64: dts: imx8mm-evk: use correct gpio-expander compatible

Commit c8713352 ("arm64: dts: imx8mm-evk: Enable pca6416 on i2c3
bus") says that the assembled expander is a PCA6416 and not a TCA6416.
No functional change since the driver handles both expanders the same
way.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>