drivers: watchdog: cop: ignore unused parameter

In install timeout api, the cfg parameter does not make sense to cop, we
can ignore it rather than return an error code to keep forward
compatibility.

Signed-off-by: Yves Wang <zhengjia.wang@nxp.com>

Author: yvesll

drivers/watchdog/wdt_mcux_cop.c

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2025 Alexandre Rey
+ * Copyright 2025 NXP
  *
  * Based on wdt_mcux_rtwdog.c, which is:
  * Copyright 2024, NXP
@@ -107,10 +108,8 @@ static int mcux_cop_install_timeout(const struct device *dev, const struct wdt_t
 	const struct mcux_cop_config *config = dev->config;
 	struct mcux_cop_data *data = dev->data;
 
-	if (cfg != NULL) {
-		LOG_ERR("Watchdog only configurable via Device Tree, cfg parameter must be NULL");
-		return -ENOTSUP;
-	}
+	/* Watchdog only configurable via Device Tree, cfg parameter does not make sense here. */
+	ARG_UNUSED(cfg);
 
 	COP_GetDefaultConfig(&data->cop_config);