Correct SPL use of WATCHDOG_AUTOSTART

This converts 1 usage of this option to the non-SPL form, since there is
no SPL_WATCHDOG_AUTOSTART defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/kontron/sl28/sl28.c b/board/kontron/sl28/sl28.c
index e78a0d5..89948e0 100644
--- a/board/kontron/sl28/sl28.c
+++ b/board/kontron/sl28/sl28.c
@@ -157,7 +157,7 @@
 	 * If the watchdog isn't enabled at reset (which is a configuration
 	 * option) disabling it doesn't hurt either.
 	 */
-	if (!CONFIG_IS_ENABLED(WATCHDOG_AUTOSTART))
+	if (!IS_ENABLED(CONFIG_WATCHDOG_AUTOSTART))
 		stop_recovery_watchdog();
 
 	return 0;