Move from memset to memset_s.

This adds the extra bounds checks and panics if there is a violation.

Change-Id: I9db3ca44be4f9c39964d912b57fe7b68e2792bc1
diff --git a/src/api.c b/src/api.c
index cd46073..ec98c22 100644
--- a/src/api.c
+++ b/src/api.c
@@ -1185,7 +1185,7 @@
 		return false;
 	}
 
-	memset(ptr, 0, size);
+	memset_s(ptr, size, 0, size);
 	arch_mm_write_back_dcache(ptr, size);
 	mm_unmap(begin, end, ppool);