cifs: fix potential null pointer use in destroy_workqueue in init_cifs error path

In the Linux kernel, the following vulnerability has been resolved:

cifs: fix potential null pointer use in destroy_workqueue in init_cifs error path

Dan Carpenter reported a Smack static checker warning:

fs/smb/client/cifsfs.c:1981 init_cifs()

error: we previously assumed 'serverclose_wq' could be null (see line 1895)

The patch which introduced the serverclose workqueue used the wrong

oredering in error paths in init_cifs() for freeing it on errors.