pam_sss: Suppress warning format-truncation
    
    src/sss_client/pam_sss.c: In function ‘send_and_receive’:
    src/sss_client/pam_sss.c:742:39: error: ‘%.*s’ directive output
      between 0 and 18446744073709551615 bytes may cause result to exceed
      ‘INT_MAX’ [-Werror=format-truncation=]
         ret = snprintf(user_msg, bufsize, "%s%s%.*s",
                                           ^~~~~~~~~~
    sssd/src/sss_client/pam_sss.c:742:39: note: assuming directive output
      of 4294967295 bytes
    
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>