net/mlx5: Fix offset of hca cap reserved field

The offending commit pushed fwd the field by two bits but
didn't increment the offset, fix that. Currently, no damage
was done b/c this is just a field name, but lets have it right.

Fixes: f32f5bd2

 ('net/mlx5: Configure cache line size for start and end padding')
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reported-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>