btrfs: zoned: fix wrong mutex unlock on failure to allocate log root tree

When syncing the log, if we fail to allocate the root node for the log
root tree:

1) We are unlocking fs_info->tree_log_mutex, but at this point we have
   not yet locked this mutex;

2) We have locked fs_info->tree_root->log_mutex, but we end up not
   unlocking it;

So fix this by unlocking fs_info->tree_root->log_mutex instead of
fs_info->tree_log_mutex.

Fixes: e75f9fd1

 ("btrfs: zoned: move log tree node allocation out of log_root_tree->log_mutex")
CC: stable@vger.kernel.org # 5.13+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>