perf: Update ABI comment

For some mysterious reason the sample_id field of PERF_RECORD_MMAP went AWOL.

Reported-by: Vince Weaver <vince@deater.net>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 file changed