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/ctree.c b/fs/btrfs/ctree.c
index 7bd12c2..2956fe2 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -181,7 +181,7 @@
 	return 0;
 }
 
-int btrfs_search_tree(const struct btrfs_root *root, struct btrfs_key *key,
+int btrfs_search_tree(const struct __btrfs_root *root, struct btrfs_key *key,
 		      struct __btrfs_path *p)
 {
 	u8 lvl, prev_lvl;