btrfs: qgroup: remove one-time use variables for quota_root checks

commit e3b0edd29737d44137fc7583a9c185abda6e23b8 upstream.

Remove some variables that are set only to be checked later, and never
used.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Harshvardhan Jha <harshvardhan.j.jha@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>