iwlwifi: fix PCIe interrupt handle return value

By accident, commit eb647644
("iwlwifi: protect use_ict with irq_lock") changed the return
value of the iwl_pcie_isr() function in case it handles an
interrupt -- it now returns IRQ_NONE instead of IRQ_HANDLED.

Put back the correct return value.

Cc: stable@vger.kernel.org
Reviewed-by: NEmmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

drivers/net/wireless/iwlwifi/pcie/rx.c

@@ -1166,6 +1166,7 @@ static irqreturn_t iwl_pcie_isr(int irq, void *data)
 	else if (test_bit(STATUS_INT_ENABLED, &trans_pcie->status) &&
 		 !trans_pcie->inta)
 		iwl_enable_interrupts(trans);
+	return IRQ_HANDLED;
 
 none:
 	/* re-enable interrupts here since we don't have anything to service. */