drm: Fix irq install error handling

The registered irq should be unregistered by free_irq() if
irq_postinstall() returns the error after request_irq() is called
successfully.

[airlied: add vga switcheroo disable]
Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_irq.c

@@ -368,6 +368,9 @@ int drm_irq_install(struct drm_device *dev)
 		mutex_lock(&dev->struct_mutex);
 		dev->irq_enabled = 0;
 		mutex_unlock(&dev->struct_mutex);
+		if (!drm_core_check_feature(dev, DRIVER_MODESET))
+			vga_client_register(dev->pdev, NULL, NULL, NULL);
+		free_irq(drm_dev_to_irq(dev), dev);
 	}
 
 	return ret;