drm/gma500: Use correct unref in the gem bo create function

This is called without dev->struct_mutex held, we need to use the
_unlocked variant.

Never caught in the wild since you'd need an evil userspace which
races a gem_close ioctl call with the in-progress open.

Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Acked-by: NPatrik Jakobsson <patrik.r.jakobsson@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1448271183-20523-17-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/gma500/gem.c

@@ -130,7 +130,7 @@ int psb_gem_create(struct drm_file *file, struct drm_device *dev, u64 size,
 		return ret;
 	}
 	/* We have the initial and handle reference but need only one now */
-	drm_gem_object_unreference(&r->gem);
+	drm_gem_object_unreference_unlocked(&r->gem);
 	*handlep = handle;
 	return 0;
 }