drivers: wifi: Fix mutex re-initialization

The mutex is used to protect RPU zephyr context which gets modified for
every interface down and up (including recovery), so, it was being
re-initialized but also used to protect down and up which is a bug.

Move the re-initialization to the driver entry so that it happens only
once and we can properly use the mutext for down and up protection.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>

Author: krish2718

drivers/wifi/nrf700x/src/fmac_main.c

@@ -632,8 +632,6 @@ enum nrf_wifi_status nrf_wifi_fmac_dev_add_zep(struct nrf_wifi_drv_priv_zep *drv
 		goto err;
 	}
 
-	k_mutex_init(&rpu_ctx_zep->rpu_lock);
-
 	return status;
 err:
 	if (rpu_ctx) {
@@ -782,6 +780,7 @@ static int nrf_wifi_drv_main_zep(const struct device *dev)
 			      nrf_wifi_scan_timeout_work);
 #endif /* CONFIG_NRF700X_RADIO_TEST */
 
+	k_mutex_init(&rpu_drv_priv_zep.rpu_ctx_zep.rpu_lock);
 	return 0;
 #ifdef CONFIG_NRF700X_RADIO_TEST
 fmac_deinit: