i40e: catch unset q_vector

Don't try to free a q_vector that hasn't been set up as it can
panic the kernel.

Change-Id: I0650cc6c441d0779788c522c790293c276d14fbc
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -3153,7 +3153,8 @@ static void i40e_vsi_free_irq(struct i40e_vsi *vsi)
 			u16 vector = i + base;
 
 			/* free only the irqs that were actually requested */
-			if (vsi->q_vectors[i]->num_ringpairs == 0)
+			if (!vsi->q_vectors[i] ||
+			    !vsi->q_vectors[i]->num_ringpairs)
 				continue;
 
 			/* clear the affinity_mask in the IRQ descriptor */