qcow2: Always use error path in l2_allocate

Just returning -errno in some cases prevents
trace_qcow2_l2_allocate_done from being executed (and, in one case, also
the unused allocated L2 table from being freed). Always going down the
error path fixes this.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/qcow2-cluster.c

@@ -200,7 +200,8 @@ static int l2_allocate(BlockDriverState *bs, int l1_index, uint64_t **table)
 
     l2_offset = qcow2_alloc_clusters(bs, s->l2_size * sizeof(uint64_t));
     if (l2_offset < 0) {
-        return l2_offset;
+        ret = l2_offset;
+        goto fail;
     }
 
     ret = qcow2_cache_flush(bs, s->refcount_block_cache);
@@ -213,7 +214,7 @@ static int l2_allocate(BlockDriverState *bs, int l1_index, uint64_t **table)
     trace_qcow2_l2_allocate_get_empty(bs, l1_index);
     ret = qcow2_cache_get_empty(bs, s->l2_table_cache, l2_offset, (void**) table);
     if (ret < 0) {
-        return ret;
+        goto fail;
     }
 
     l2_table = *table;