perf tools: Cleanup realloc use

The if branch is completely unnecessary since 'realloc' handles NULL
pointers for the first parameter.

This is really only a cleanup and submitted mainly to prevent
proliferation of bad practices.

Signed-off-by: Ulrich Drepper <drepper@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/201204231304.q3ND4TFe020805@drepperk.user.openhosting.com


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