perf callchains: Switch from strtok() to strtok_r() when parsing options

Trying to keep everything reentrant.

Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/n/tip-rdce0p2k9e1b4qnrb8ki9mtf@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>