mm: cma: alloc_contig_range: return early for err path

If start_isolate_page_range() failed, unset_migratetype_isolate() has been
done inside it.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

mm/page_alloc.c

@@ -5825,7 +5825,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 	ret = start_isolate_page_range(pfn_max_align_down(start),
 				       pfn_max_align_up(end), migratetype);
 	if (ret)
-		goto done;
+		return ret;
 
 	ret = __alloc_contig_migrate_range(&cc, start, end);
 	if (ret)