cifs: change && to ||

This is a typo, if pvolume_info were NULL it would oops.

This function is used in clean up and error handling.  The current code
never passes a NULL pvolume_info, but it could pass a NULL *pvolume_info
if the kmalloc() failed.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>