perf machine: Use map as success in ip__resolve_ams

When trying to map a bunch of instruction addresses to their respective
threads, I kept getting a lot of bogus entries [I forget the exact
reason as I patched my code months ago].

Looking through ip__resolve_ams, I noticed the check for

  if (al.sym)

and realized, most times I have an al.map definition but sometimes an
al.sym is undefined.  In the cases where al.sym is undefined, the loop
keeps going even though a valid al.map exists.

Modify this check to use the more reliable al.map.  This fixed my bogus
entries.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1393386227-149412-2-git-send-email-dzickus@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>