samples: subsys: ipc: openamp: correct mpu attribution

- Set ocram2_sh_mem attribution as ATTR_MPU_RAM_NOCACHE

Signed-off-by: Lucien Zhao <[email protected]>

Author: lucien-nxp

samples/subsys/ipc/openamp/boards/mimxrt1180_evk_mimxrt1189_cm33.overlay

@@ -22,7 +22,7 @@
 		compatible = "zephyr,memory-region", "mmio-sram";
 		reg = <0x20500000 DT_SIZE_K(32)>;
 		zephyr,memory-region = "OCRAM2_SH_MEM";
-		zephyr,memory-attr = <DT_MEM_ARM(ATTR_MPU_IO)>;
+		zephyr,memory-attr = <DT_MEM_ARM(ATTR_MPU_RAM_NOCACHE)>;
 	};
 
 	mailbox_a: ipm-mbox {