Revert "drm/i915: Exit cherryview_irq_handler() after one pass"

This reverts commit 9dbaab56.

Turns out it was a bad idea and was fixed up "properly" in 4.7 but those
patches are too big to put into 4.6, so let's just revert it for now.
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Peter Frühberger <peter.fruehberger@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/i915/i915_irq.c

@@ -1829,7 +1829,7 @@ static irqreturn_t cherryview_irq_handler(int irq, void *arg)
 	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
 	disable_rpm_wakeref_asserts(dev_priv);
 
-	do {
+	for (;;) {
 		master_ctl = I915_READ(GEN8_MASTER_IRQ) & ~GEN8_MASTER_IRQ_CONTROL;
 		iir = I915_READ(VLV_IIR);
 
@@ -1857,7 +1857,7 @@ static irqreturn_t cherryview_irq_handler(int irq, void *arg)
 
 		I915_WRITE(GEN8_MASTER_IRQ, DE_MASTER_IRQ_CONTROL);
 		POSTING_READ(GEN8_MASTER_IRQ);
-	} while (0);
+	}
 
 	enable_rpm_wakeref_asserts(dev_priv);