perf thread_map: Fix the sizeof() calculation for map entries

perf thread_map: Fix the sizeof() calculation for map entries

When we started adding extra stuff per array entry, growing the size of
those entries to more than sizeof(pid_t), we had to convert those sizeof
operations to the more robust sizeof(map->map[0]) idiom, that is future
proof, i.e. if/when we add more stuff to those entries, that expression
will produce the new per-entry size.

And besides that, we need to zero out those extra fields, that sometimes
may not get filled, like when we couldn't care less about the comms,
since we don't need those, but since we will try freeing it at
thread_map__delete(), we better fix it.

That is why a thread_map__realloc() was provided.

But that method wasn't used in thread_map__new_by_uid(), fix it.

Reported-by: Ingo Molnar <mingo@kernel.org>
Fixes: 792402fd5c0a ("perf thrad_map: Add comm string into array")
Fixes: 9d7e8c3a96e5 ("perf tools: Add thread_map__(alloc|realloc) helpers")
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-6a0swlm6m8lnu3wpjv284hkb@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>