sss_client/idmap/common_ex.c: fix sss_nss_timedlock() to return errno
    
    sss_nss_timedloc() should return errno, but returns -1 if clock_gettime(2) fails.
    Fix sss_nss_timedlock() to return errno if clock_gettime(2) fails.
    
    Reviewed-by: Alexey Tikhonov <atikhono@redhat.com>