btrfs: fix warning on uninit variable in btrfs_finish_chunk_alloc

map->num_stripes really can't be zero, but just in case.

Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a37cc04..a114b7b 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4794,7 +4794,7 @@
 	u64 dev_offset;
 	u64 stripe_size;
 	int i = 0;
-	int ret;
+	int ret = 0;
 
 	em_tree = &extent_root->fs_info->mapping_tree.map_tree;
 	read_lock(&em_tree->lock);