perf report: Make --sort comm,dso,symbol the default

If you're doing performance testing, you're interested in the
symbols anyway so lets make "--sort comm,dso,symbol" the
default sort option.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: acme@redhat.com
LKML-Reference: <1249467921-10450-1-git-send-email-penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>