perf parse-events: Fix reading of invalid memory in event parsing

ADD_CONFIG_TERM accesses term->weak, however, in get_config_chgs this
value is accessed outside of the list_for_each_entry and references
invalid memory. Add an argument for ADD_CONFIG_TERM for weak and set it
to false in the get_config_chgs case.

This bug was cause by clang's address sanitizer and libfuzzer. It can be
reproduced with a command line of:

  perf stat -a -e i/bs,tsc,L2/o

Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: clang-built-linux@googlegroups.com
Link: http://lore.kernel.org/lkml/20200307073121.203816-1-irogers@google.com


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