Revert "rt2800pci: handle spurious interrupts"

This reverts commit 4ba7d999.

The original patch was a misguided attempt to improve performance on
some hardware that is apparently prone to spurious interrupt generation.
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800pci.c

@@ -880,13 +880,8 @@ static irqreturn_t rt2800pci_interrupt(int irq, void *dev_instance)
 	rt2x00pci_register_read(rt2x00dev, INT_SOURCE_CSR, &reg);
 	rt2x00pci_register_write(rt2x00dev, INT_SOURCE_CSR, reg);
 
-	/*
-	 * Some devices can generate interrupts with empty CSR register, we
-	 * "handle" such irq's to prevent interrupt controller treat them as
-	 * spurious interrupts and disable irq line.
-	 */
 	if (!reg)
-		return IRQ_HANDLED;
+		return IRQ_NONE;
 
 	if (!test_bit(DEVICE_STATE_ENABLED_RADIO, &rt2x00dev->flags))
 		return IRQ_HANDLED;