btrfs: set root to null in btrfs_search_path_in_tree_user

We could potentially have root uninitialized in some cases, so this will
cause problems with btrfs_put_root.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>

fs/btrfs/ioctl.c

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0bd6910..92cb38c 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2388,7 +2388,7 @@ static int btrfs_search_path_in_tree_user(struct inode *inode,
 	unsigned long item_len;
 	struct btrfs_inode_ref *iref;
 	struct btrfs_root_ref *rref;
-	struct btrfs_root *root;
+	struct btrfs_root *root = NULL;
 	struct btrfs_path *path;
 	struct btrfs_key key, key2;
 	struct extent_buffer *leaf;