drm/gem-shmem: Add import attachment warning to locked pin function

Commit ec144244 ("drm/gem-shmem: Acquire reservation lock in GEM
pin/unpin callbacks") moved locking DRM object's dma reservation to
drm_gem_shmem_object_pin, and made drm_gem_shmem_pin_locked public, so
we need to make sure the not-imported check warning is also added to
the latter.

Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Fixes: a7802784 ("drm/gem: Acquire reservation lock in drm_gem_{pin/unpin}()")
Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240523113236.432585-4-adrian.larumbe@collabora.com

drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -233,6 +233,8 @@ int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
 
 	dma_resv_assert_held(shmem->base.resv);
 
+	drm_WARN_ON(shmem->base.dev, shmem->base.import_attach);
+
 	ret = drm_gem_shmem_get_pages(shmem);
 
 	return ret;