net/mlx5: EQ, Use the right place to store/read IRQ affinity hint

Currently the cpu affinity hint mask for completion EQs is stored and
read from the wrong place, since reading and storing is done from the
same index, there is no actual issue with that, but internal irq_info
for completion EQs stars at MLX5_EQ_VEC_COMP_BASE offset in irq_info
array, this patch changes the code to use the correct offset to store
and read the IRQ affinity hint.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>