perf stat: Fix saved values rbtree lookup

perf stat: Fix saved values rbtree lookup

The stat shadow saved values rbtree is indexed by a pointer.  Fix the
comparison function:

- We cannot return a pointer delta as an int because that loses bits on
  64bit.

- Doing pointer arithmetic on the struct pointer only works if the
  objects are spaced by the multiple of the object size, which is not
  guaranteed for individual malloc'ed object

Replace it with a proper comparison.

This fixes various problems with values not being found.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20170724234015.5165-4-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>