net/mlx4_core: Correcly update the mtt's offset in the MR re-reg flow

Previously, mlx4_mt_rereg_write filled the MPT's entity_size with the
old MTT's page shift, which could result in using an incorrect offset.
Fix the initialization to be after we calculate the new MTT offset.

In addition, assign mtt order to -1 after calling mlx4_mtt_cleanup. This
is necessary in order to mark the MTT as invalid and avoid freeing it later.

Fixes: e630664c ('mlx4_core: Add helper functions to support MR re-registration')
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>