net/mlx5: Fix wrong comment

A control irq may be allocated from the parent device's pool in case
there is no SF dedicated pool. This could happen when there are not
enough vectors available for SFs.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>