net/mlx5: Check for invalid vector index on EQ creation

Currently, mlx5 driver does not enforce vector index to be lower than
the maximum number of supported completion vectors when requesting a
new completion EQ. Thus, mlx5_comp_eqn_get() fails when trying to
acquire an IRQ with an improper vector index.

To prevent the case above, enforce that vector index value is
valid and lower than maximum in mlx5_comp_eqn_get() before handling the
request.

Fixes: f14c1a14 ("net/mlx5: Allocate completion EQs dynamically")
Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>