perf: Missing field in PERF_RECORD_SAMPLE documentation

While trying to write a perf_event/mmap test for my perf_event
test-suite I came across a missing field description in the
PERF_RECORD_SAMPLE documentation in perf_event.h
Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
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/alpine.DEB.2.02.1301081439300.24507@vincent-weaver-1.um.maine.eduSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

include/uapi/linux/perf_event.h

@@ -579,6 +579,7 @@ enum perf_event_type {
 	 *	{ u32			size;
 	 *	  char                  data[size];}&& PERF_SAMPLE_RAW
 	 *
+	 *	{ u64                   nr;
 	 *        { u64 from, to, flags } lbr[nr];} && PERF_SAMPLE_BRANCH_STACK
 	 *
 	 * 	{ u64			abi; # enum perf_sample_regs_abi