VAS: use local_free to free local_alloc memory

free() asserts because local_alloc() doesn't allocate from the skiboot
heap region. Fix this by using local_free().

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
diff --git a/hw/vas.c b/hw/vas.c
index 96ca055..aa3ae33 100644
--- a/hw/vas.c
+++ b/hw/vas.c
@@ -428,7 +428,7 @@
 static inline void free_wcbs(struct proc_chip *chip)
 {
 	if (chip->vas->wcbs) {
-		free((void *)chip->vas->wcbs);
+		local_free((void *)chip->vas->wcbs);
 		chip->vas->wcbs = 0ULL;
 	}
 }
@@ -466,7 +466,7 @@
 	return OPAL_SUCCESS;
 
 out:
-	free((void *)wcbs);
+	local_free((void *)wcbs);
 	return rc;
 }