We were calling perf_session__process_machines(), that would first pass
the struct machine associated with the host to the provided callback,
perf_event__synthesize_guest_os() that would test if it was the host and
if so wouldn't do anything.

Ditch this contraption, just call directly machines__process with the
list of guests.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-x65vsxgzg4dvo3zqohtrrb9o@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>