i40evf: check for msix_entries null dereference

It is possible for msix_entries to be freed by a previous suspend/remove
before a VF is closed.  This patch fixes the issue by checking for NULL
before dereferencing msix_entries and returning early in the case where
it is NULL within the i40evf_close code path.  Without this patch it is
possible to trigger a kernel panic through NULL dereference.

Change-ID: I92a2746e82533a889e25f91578eac9abd0388ae2
Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40evf/i40evf_main.c

@@ -631,6 +631,9 @@ static void i40evf_free_traffic_irqs(struct i40evf_adapter *adapter)
 {
 	int vector, irq_num, q_vectors;
 
+	if (!adapter->msix_entries)
+		return;
+
 	q_vectors = adapter->num_msix_vectors - NONQ_VECS;
 
 	for (vector = 0; vector < q_vectors; vector++) {
@@ -1443,6 +1446,9 @@ static void i40evf_free_q_vectors(struct i40evf_adapter *adapter)
  **/
 void i40evf_reset_interrupt_capability(struct i40evf_adapter *adapter)
 {
+	if (!adapter->msix_entries)
+		return;
+
 	pci_disable_msix(adapter->pdev);
 	kfree(adapter->msix_entries);
 	adapter->msix_entries = NULL;