arm64: dts: imx93: correct s4mu interrupt names

Per binding doc, interrupt names should be tx and rx.

Fixes: 0dfb380d ("arm64: dts: imx93: add s4 mu node")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>