net/mlx5: Fix order of functions in mlx5_irq_detach_nb()

Change order of functions in mlx5_irq_detach_nb() so it will be
a mirror of mlx5_irq_attach_nb.

Fixes: 71e084e2

 ("net/mlx5: Allocating a pool of MSI-X vectors for SFs")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>