drm/nouveau: do not unpin in nouveau_gem_object_del

This should no longer be required, and is harmful for framebuffer pinning.
Also add a warning if unpin causes the pin count to drop below 0.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_gem.c

@@ -50,12 +50,6 @@ nouveau_gem_object_del(struct drm_gem_object *gem)
 		return;
 	nvbo->gem = NULL;
 
-	/* Lockdep hates you for doing reserve with gem object lock held */
-	if (WARN_ON_ONCE(nvbo->pin_refcnt)) {
-		nvbo->pin_refcnt = 1;
-		nouveau_bo_unpin(nvbo);
-	}
-
 	if (gem->import_attach)
 		drm_prime_gem_destroy(gem, nvbo->bo.sg);