perf tools: Handle allocation failures gracefully

The callers of perf_read_values__enlarge_counters() already propagate
errors, so just print some debug diagnostics and handle allocation
failures gracefully, not trying to do silly things like 'a =
realloc(a)'.

Link: http://lkml.kernel.org/n/tip-nsmmh7uzpg35rzcl9nq7yztp@git.kernel.org


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