board: sl28: fix linking with disabled watchdog

We don't have a reference to the driver used by
uclass_get_device_by_driver() in stop_recovery_watchdog(). Fix it by not
calling that function if the watchdog driver isn't enabled.

Signed-off-by: Michael Walle <mwalle@kernel.org>
Reviewed-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/board/kontron/sl28/sl28.c b/board/kontron/sl28/sl28.c
index adfec8b..0baf5c6 100644
--- a/board/kontron/sl28/sl28.c
+++ b/board/kontron/sl28/sl28.c
@@ -156,7 +156,8 @@
 	 * If the watchdog isn't enabled at reset (which is a configuration
 	 * option) disabling it doesn't hurt either.
 	 */
-	if (!IS_ENABLED(CONFIG_WATCHDOG_AUTOSTART))
+	if (IS_ENABLED(CONFIG_WDT_SL28CPLD) &&
+	    !IS_ENABLED(CONFIG_WATCHDOG_AUTOSTART))
 		stop_recovery_watchdog();
 
 	return 0;