drm/radeon: Fix radeon_irq_kms_pflip_irq_get/put() imbalance

Fixes a regression in 3.16-rc1 compared to 3.15.

The unbalanced calls would presumably result in the page flip interrupts
never getting disabled once they are enabled.

Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_display.c

@@ -360,7 +360,7 @@ void radeon_crtc_handle_flip(struct radeon_device *rdev, int crtc_id)
 
 	drm_vblank_put(rdev->ddev, radeon_crtc->crtc_id);
 	radeon_fence_unref(&work->fence);
-	radeon_irq_kms_pflip_irq_get(rdev, work->crtc_id);
+	radeon_irq_kms_pflip_irq_put(rdev, work->crtc_id);
 	queue_work(radeon_crtc->flip_queue, &work->unpin_work);
 }