[nrf fromlist] boards: nordic: Fix the label for nRF70 SR co-existence

The co-existence modules expect a common and fixed name, so, rename it
to avoid churn.

Upstream PR: zephyrproject-rtos/zephyr#80474

Signed-off-by: Chaitanya Tata <[email protected]>

Author: krish2718

boards/nordic/nrf7002dk/nrf7002dk_nrf5340_cpunet.dts

@@ -82,7 +82,7 @@
 			   <21 0 &gpio1 3 0>;	/* D15 */
 	};
 
-	nrf70: coex {
+	nrf_radio_coex: coex {
 		status = "okay";
 		compatible = "nordic,nrf7002-coex";