lib/cifs_idmap_sss: fixed unaligned mem access
    
    Fixed following warning:
    ```
    lib/cifs_idmap_sss/cifs_idmap_sss.c: In function ‘sss_sid_to_id’:
    lib/cifs_idmap_sss/cifs_idmap_sss.c:221:47: warning: taking address
    of packed member of ‘struct cifs_uxid’ may result in an unaligned
    pointer value [-Waddress-of-packed-member]
    
    err = sss_nss_getidbysid(sid, (uint32_t *)&cuxid->id.uid, &id_type);
    ```
    
    Actually there are two issues:
    1) Packed `cifs_uxid::id.uid` may be unaligned thus generating run time
    error on some architectures (as compiler complains);
    2) In theory size of `uid_t` may be different than size of `uint32_t`
    thus resulting in corruption of `cifs_uxid` content.
    
    Proposed patch is not ideal due to `(uid_t)uid` cast but solves most
    of issues with minimal effor. Proper solution would require patching of
    `sss_nss_getidbysid()` and all underlying functions for no good reason.
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>