drivers: watchdog: stm32 iwdg: explicit single channel

The STM32 IWDG is a single channel watchdog, and therefore should be
returning `-ENOMEM` when a user attempt to install additional timeouts,
instead of overwriting previous values.

Signed-off-by: Jordan Yates <[email protected]>

Author: JordanYates

drivers/watchdog/wdt_iwdg_stm32.c

@@ -151,6 +151,10 @@ static int iwdg_stm32_install_timeout(const struct device *dev,
 	if (config->callback != NULL) {
 		return -ENOTSUP;
 	}
+	if (data->reload) {
+		/* Timeout has already been configured */
+		return -ENOMEM;
+	}
 
 	/* Calculating parameters to be applied later, on setup */
 	iwdg_stm32_convert_timeout(timeout, &prescaler, &reload);