Btrfs-progs: pass properly formated key to read_fs_root

We have a BUG_ON() in read_fs_root that expects key->offset == (u64)-1.  Restore
will just pass in the location it reads out of the inode if it has a subvol
reference and pass that in, which doesn't have offset == (u64)-1, so it causes
restore blow up.  This was reported in bugzilla and this patch fixed the
problem.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

cmds-restore.c

@@ -708,6 +708,7 @@ static int search_dir(struct btrfs_root *root, struct btrfs_key *key,
 					goto next;
 				}
 
+				location.offset = (u64)-1;
 				search_root = btrfs_read_fs_root(root->fs_info,
 								 &location);
 				if (IS_ERR(search_root)) {