IB/mlx4: Fix the SQ size of an RC QP

When calculating the required size of an RC QP send queue, leave
enough space for masked atomic operations, which require more space than
"regular" atomic operation.

Fixes: 6fa8f719 ("IB/mlx4: Add support for masked atomic operations")
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Reviewed-by: Jack Morgenstein <jackm@mellanox.co.il>
Reviewed-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>