perf tools: Get current comm instead of last one

At insert time, a hist entry should reference comm at the time otherwise
it'll get the last comm anyway.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/n/tip-n6pykiiymtgmcjs834go2t8x@git.kernel.org
[ Fixed up const pointer issues ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>