net/mlx5: Fix reserved at offset in hca_cap register

A member of struct mlx5_ifc_cmd_hca_cap_bits has been mistakenly
assigned the wrong reserved_at offset value. Correct it to align to the
right value, thus avoid future miscalculation.

Signed-off-by: Lama Kayal <lkayal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>