net/mlx5: Fix mlx5_ifc_mtpps_reg_bits structure size

Fix miscalculation in reserved_at_1a0 field.

Fixes: ee7f1220 ('net/mlx5e: Implement 1PPS support')
Signed-off-by: Eugenia Emantayev <eugenia@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>