perf inject: Mark a dso if it's used

Otherwise they will be not written in an output file.

Signed-off-by: Andrew Vagin <avagin@openvz.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1344344165-369636-5-git-send-email-avagin@openvz.org


[ committer note: Fixed up wrt changes made in the immediate previous patches ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>