drm/virtio: Fix error code in virtio_gpu_object_shmem_init()

stable inclusion
from stable-v5.10.173
commit c5fe3fba1b7bfecb6f17f93a433782b8500fe377
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6IKWF
CVE: CVE-2023-22998

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c5fe3fba1b7bfecb6f17f93a433782b8500fe377

--------------------------------

In virtio_gpu_object_shmem_init() we are passing NULL to PTR_ERR, which
is returning 0/success.

Fix this by storing error value in 'ret' variable before assigning
shmem->pages to NULL.

Found using static analysis with Smatch.

Fixes: 64b88afb ("drm/virtio: Correct drm_gem_shmem_get_sg_table() error handling")
Signed-off-by: NHarshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: NDmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NGuo Mengqi <guomengqi3@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>

drivers/gpu/drm/virtio/virtgpu_object.c

@@ -159,8 +159,9 @@ static int virtio_gpu_object_shmem_init(struct virtio_gpu_device *vgdev,
 	shmem->pages = drm_gem_shmem_get_sg_table(&bo->base.base);
 	if (IS_ERR(shmem->pages)) {
 		drm_gem_shmem_unpin(&bo->base.base);
+		ret = PTR_ERR(shmem->pages);
 		shmem->pages = NULL;
-		return PTR_ERR(shmem->pages);
+		return ret;
 	}
 
 	if (use_dma_api) {