powerpc/eeh-powernv: Fix unbalanced IRQ warning

pnv_eeh_next_error() re-enables the eeh opal event interrupt but it
gets called from a loop if there are more outstanding events to
process, resulting in a warning due to enabling an already enabled
interrupt. Instead the interrupt should only be re-enabled once the
last outstanding event has been processed.
Tested-by: Daniel Axtens <dja@axtens.net>
Reported-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Alistair Popple <alistair@popple.id.au>
Acked-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/eeh-powernv.c

@@ -1478,7 +1478,7 @@ static int pnv_eeh_next_error(struct eeh_pe **pe)
 	}
 
 	/* Unmask the event */
-	if (eeh_enabled())
+	if (ret == EEH_NEXT_ERR_NONE && eeh_enabled())
 		enable_irq(eeh_event_irq);
 
 	return ret;