btreplay: Fix typo in scaling up the dynamic cpu set size.

btreplay: Fix typo in scaling up the dynamic cpu set size.

In get_ncpus, we default to using 4096 CPUs if _SC_NPROCESSORS_CONF isn't
enabled.  If that is insufficient, sched_getaffinity will fail and we
retry after doubling the size of the cpu_set_t allocation.  There's a typo
in there that means we don't actually double the size and will loop
forever allocating the same sized cpu_set_t instead.

Signed-off-by: Josef Cejka <jcejka@suse.com>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>