commit: Don't use error_abort in commit_start

bdrv_set_backing_hd failure needn't be abort. Since we already have
error parameter, use it.
Signed-off-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/commit.c

@@ -316,8 +316,20 @@ void commit_start(const char *job_id, BlockDriverState *bs,
         goto fail;
     }
 
-    bdrv_set_backing_hd(commit_top_bs, top, &error_abort);
-    bdrv_set_backing_hd(overlay_bs, commit_top_bs, &error_abort);
+    bdrv_set_backing_hd(commit_top_bs, top, &local_err);
+    if (local_err) {
+        bdrv_unref(commit_top_bs);
+        commit_top_bs = NULL;
+        error_propagate(errp, local_err);
+        goto fail;
+    }
+    bdrv_set_backing_hd(overlay_bs, commit_top_bs, &local_err);
+    if (local_err) {
+        bdrv_unref(commit_top_bs);
+        commit_top_bs = NULL;
+        error_propagate(errp, local_err);
+        goto fail;
+    }
 
     s->commit_top_bs = commit_top_bs;
     bdrv_unref(commit_top_bs);