perf machine: Fix machine.vmlinux_maps to make sure to clear the old one

perf machine: Fix machine.vmlinux_maps to make sure to clear the old one

Fix machine.vmlinux_maps to make sure to clear the old one if it is
renewal. This can leak the previous maps on the vmlinux_maps because
those are just overwritten.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20151209021133.10245.93730.stgit@localhost.localdomain
[ Simplified the memset, same end result ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>