Running 'perf kvm --host --guest --guestmount /tmp/guestmount record -a -g -- sleep 2'

Was resulting in a segfault. For event type PERF_RECORD_MMAP,
event->ip.pid is being used in perf_session__find_machine_for_cpumode,
which is not correct.

The event->ip.pid field happens to be 0 in this case and results in
returning a NULL machine object. Finally, access to self->pid in
machine__mmap_name, results in a segfault later.

For PERF_RECORD_MMAP type, pass event->mmap.pid.
Signed-off-by: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Tested-by: David Ahern <dsahern@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20120409081835.10576.22018.stgit@abhimanyu.in.ibm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>