perf jevents: Parse eventcode as number

The next patch needs to modify event code. Previously eventcode was just
passed through as a string. Now parse it as a number.

v2: Don't special case 0

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20170128020345.19007-2-andi@firstfloor.org


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