drm/shmem-helper: Add missing vunmap on error

commit df4aaf0 upstream.

The vmapping of dma-buf may succeed, but DRM SHMEM rejects the IOMEM
mapping, and thus, drm_gem_shmem_vmap_locked() should unvmap the IOMEM
before erroring out.

Cc: stable@vger.kernel.org
Fixes: 49a3f51 ("drm/gem: Use struct dma_buf_map in GEM vmap ops and convert GEM backends")
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220630200058.1883506-2-dmitry.osipenko@collabora.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -275,6 +275,7 @@ static int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem, struct
 		ret = dma_buf_vmap(obj->import_attach->dmabuf, map);
 		if (!ret) {
 			if (WARN_ON(map->is_iomem)) {
+				dma_buf_vunmap(obj->import_attach->dmabuf, map);
 				ret = -EIO;
 				goto err_put_pages;
 			}