IB/mlx4: Put non zero value in max_ah device attribute

Use INT_MAX since this is the max value the attribute can hold, though
hardware capability is unlimited.

Fixes: 225c7b1f

 ('IB/mlx4: Add a driver Mellanox ConnectX InfiniBand adapters')
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Daniel Jurgens <danielj@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>