perf top: Always show the DSO column, even if its all the same

perf top: Always show the DSO column, even if its all the same

Ingo found it confusing, and I agree with that, for 'perf
report' its OK because it is static, but for a tool refreshing
it the eventual switch from column to summary at the top may
seem confusing.

Suggested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1259071517-3242-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>