perf tools: remove redundant checks from _sort__sym_cmp

perf tools: remove redundant checks from _sort__sym_cmp

We already check that sym_l and sum_r are non-NULLs, no need to do it
twice.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1356030701-16284-12-git-send-email-sasha.levin@oracle.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>