spl: Avoid #ifdef with CONFIG_SPL_SYS_MALLOC

Use IF_ENABLED_INT() to avoid needing to use the preprocessor.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl.c b/common/spl/spl.c
index 0f45336..a58b070 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -750,10 +750,10 @@
 
 	spl_set_bd();
 
-#if defined(CONFIG_SPL_SYS_MALLOC)
-	mem_malloc_init(SPL_SYS_MALLOC_START, CONFIG_SPL_SYS_MALLOC_SIZE);
-	gd->flags |= GD_FLG_FULL_MALLOC_INIT;
-#endif
+	if (IS_ENABLED(CONFIG_SPL_SYS_MALLOC)) {
+		mem_malloc_init(SPL_SYS_MALLOC_START, SPL_SYS_MALLOC_SIZE);
+		gd->flags |= GD_FLG_FULL_MALLOC_INIT;
+	}
 	if (!(gd->flags & GD_FLG_SPL_INIT)) {
 		if (spl_init())
 			hang();