perf c2c: Keep struct hist_entry at the end of struct c2c_hist_entry

perf c2c: Keep struct hist_entry at the end of struct c2c_hist_entry

Exactly as the comment just before 'struct c2c_hist_entry" says, i.e.
the last entry in struct hist_entry is a zero length array, that when
allocating space for hist_entry gets extra space if callchains are in
use, which, if hist_entry is not at the end of c2c_hist_entry, the
members after it gets corrupted when callchains get added to the rb
trees collecting them, etc.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jin Yao <yao.jin@linux.intel.com>
Fixes: 7f834c2e84bb ("perf c2c report: Display node for cacheline address")
Link: http://lkml.kernel.org/n/tip-bh0ke4fh2ygpj3yowna7o1di@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>