mlx5: avoid 64-bit division

Commit 25c13324 ("IB/mlx5: Add steering SW ICM device memory type")
breaks i386 build by introducing three 64-bit divisions. As the divisor is
MLX5_SW_ICM_BLOCK_SIZE() which is always a power of 2, we can replace the
division with bit operations.

Fixes: 25c13324

 ("IB/mlx5: Add steering SW ICM device memory type")
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>