drm/bochs: Fix connector leak during driver unload

When unloading the bochs-drm driver, a warning message is printed by
drm_mode_config_cleanup() because a reference is still held to one of
the drm_connector structs.

Correct this by calling drm_atomic_helper_shutdown() in
bochs_pci_remove().

Fixes: 6579c395 ("drm/bochs: atomic: switch planes to atomic, wire up helpers.")
Signed-off-by: Sam Bobroff <sbobroff@linux.ibm.com>
Link: http://patchwork.freedesktop.org/patch/msgid/93b363ad62f4938d9ddf3e05b2a61e3f66b2dcd3.1558416473.git.sbobroff@linux.ibm.comSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/bochs/bochs_drv.c

@@ -10,6 +10,7 @@
 #include <linux/slab.h>
 #include <drm/drm_fb_helper.h>
 #include <drm/drm_probe_helper.h>
+#include <drm/drm_atomic_helper.h>
 
 #include "bochs.h"
 
@@ -158,6 +159,7 @@ static void bochs_pci_remove(struct pci_dev *pdev)
 {
 	struct drm_device *dev = pci_get_drvdata(pdev);
 
+	drm_atomic_helper_shutdown(dev);
 	drm_dev_unregister(dev);
 	bochs_unload(dev);
 	drm_dev_put(dev);