perf annotate: Fix sizeof_sym_hist overflow issue

The annotated_source::sizeof_sym_hist could easily overflow int size,
resulting in crash in __symbol__inc_addr_samples.

Changing its type int size_t as was probably intended from beginning
based on the initialization code in symbol__alloc_hist.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1444068369-20978-4-git-send-email-jolsa@kernel.org


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