drm/vmwgfx: Use list_move_tail instead of list_del/list_add_tail in vmwgfx_cmdbuf.c

Using list_move_tail() instead of list_del() + list_add_tail() in vmwgfx_cmdbuf.c.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210609071803.1347254-1-libaokun1@huawei.com