Move sizeof to second argument in calloc calls

../dix/main.c:165:42: warning: ‘calloc’ sizes specified with ‘sizeof’ in the
 earlier argument and not in the later argument [-Wcalloc-transposed-args]
  165 |             serverClient = calloc(sizeof(ClientRec), 1);
      |                                          ^~~~~~~~~
../dix/main.c:165:42: note: earlier argument should specify number of
 elements, later size of each element