powerpc/eeh: Check handle_eeh_events() return value

Function eeh_event_handler() dereferences the pointer returned by
handle_eeh_events() without checking, causing a crash if NULL was
returned, which is expected in some situations.

This patch fixes this bug by checking for the value returned by
handle_eeh_events() before dereferencing it.
Signed-off-by: Kleber Sacilotto de Souza <klebers@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: stable@vger.kernel.org [v3.4+]

arch/powerpc/platforms/pseries/eeh_event.c

@@ -85,8 +85,10 @@ static int eeh_event_handler(void * dummy)
 	set_current_state(TASK_INTERRUPTIBLE);	/* Don't add to load average */
 	edev = handle_eeh_events(event);
 
+	if (edev) {
 		eeh_clear_slot(eeh_dev_to_of_node(edev), EEH_MODE_RECOVERING);
 		pci_dev_put(edev->pdev);
+	}
 
 	kfree(event);
 	mutex_unlock(&eeh_event_mutex);