perf bench numa: Fix assertion for nodes bitfield

Comparing bits and bytes in numa benchmark assertion

I hit the issue on two socket Power8 machine presenting its numa nodes
as 0,1,16,17 (according to numactl). Therefore I got error (and hang of
parent process):

    perf: bench/numa.c:296: bind_to_memnode: Assertion `!(g->p.nr_nodes > (int)sizeof(nodemask))' failed.

This is obviously false positive. We can fit all the 18 nodes into
bitfield of 8 bytes (long on 64b architecture).

Signed-off-by: Jakub Jelen <jakuje@gmail.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jakub Jelen <jjelen@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: trivial@kernel.org
Link: http://lkml.kernel.org/r/1458388687-24421-1-git-send-email-jakuje@gmail.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>