fs: btrfs: Rename btrfs_root to __btrfs_root

This is to avoid naming conflicts between extent buffer based
btrfs_root.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Marek BehĂșn <marek.behun@nic.cz>
diff --git a/fs/btrfs/root.c b/fs/btrfs/root.c
index 9b5f645..a424966 100644
--- a/fs/btrfs/root.c
+++ b/fs/btrfs/root.c
@@ -31,7 +31,7 @@
 	}
 }
 
-int btrfs_find_root(u64 objectid, struct btrfs_root *root,
+int btrfs_find_root(u64 objectid, struct __btrfs_root *root,
 		    struct btrfs_root_item *root_item)
 {
 	struct __btrfs_path path;