dm: core: Allow devres to be disabled in SPL

At present if devres is enabled in U-Boot proper it is enabled in SPL.
We don't normally want it there, so disable it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Angus Ainslie <angus@akkea.ca>
diff --git a/include/dm/device.h b/include/dm/device.h
index cb52a09..3d8961f 100644
--- a/include/dm/device.h
+++ b/include/dm/device.h
@@ -184,7 +184,7 @@
 #if CONFIG_IS_ENABLED(OF_REAL)
 	ofnode node_;
 #endif
-#ifdef CONFIG_DEVRES
+#if CONFIG_IS_ENABLED(DEVRES)
 	struct list_head devres_head;
 #endif
 #if CONFIG_IS_ENABLED(DM_DMA)