net/mlx5e: SHAMPO, Fix constant expression result

mlx5e_build_shampo_hd_umr uses counters i and index incorrectly
as unsigned, thus the err state err_unmap could stuck in endless loop.
Change i to int to solve the first issue.
Reduce index check to solve the second issue, the caller function
validates that index could not rotate.

Fixes: 64509b05 ("net/mlx5e: Add data path for SHAMPO feature")
Signed-off-by: Ben Ben-Ishay <benishay@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>