fm10k: Cleanup exception handling for mailbox interrupt

BugLink: http://bugs.launchpad.net/bugs/1536475

This patch addresses two issues.

First is the fact that the fm10k_mbx_free_irq was assuming msix_entries was
valid and that will not always be the case.  As such we need to add a check
for if it is NULL.

Second is the fact that we weren't freeing the IRQ if the mailbox API
returned an error on trying to connect.
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Reviewed-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Krishneil Singh <Krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit e00e23bc)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/net/ethernet/intel/fm10k/fm10k_pci.c

@@ -1124,6 +1124,10 @@ void fm10k_mbx_free_irq(struct fm10k_intfc *interface)
 	struct fm10k_hw *hw = &interface->hw;
 	int itr_reg;
 
+	/* no mailbox IRQ to free if MSI-X is not enabled */
+	if (!interface->msix_entries)
+		return;
+
 	/* disconnect the mailbox */
 	hw->mbx.ops.disconnect(hw, &hw->mbx);
 
@@ -1446,10 +1450,15 @@ int fm10k_mbx_request_irq(struct fm10k_intfc *interface)
 		err = fm10k_mbx_request_irq_pf(interface);
 	else
 		err = fm10k_mbx_request_irq_vf(interface);
+	if (err)
+		return err;
 
 	/* connect mailbox */
-	if (!err)
-		err = hw->mbx.ops.connect(hw, &hw->mbx);
+	err = hw->mbx.ops.connect(hw, &hw->mbx);
+
+	/* if the mailbox failed to connect, then free IRQ */
+	if (err)
+		fm10k_mbx_free_irq(interface);
 
 	return err;
 }