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: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Guo Mengqi <guomengqi3@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>