perf tools: Fix syntax in documentation

Fix trivial syntax in perf-events user-space tools
documentation.

Signed-off-by: Zeev Tarantov <zeev.tarantov@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <12d7e64c0911081811i7e5b466cu6706ff6ab3e70db4@mail.gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/Documentation/perf-report.txt

@@ -24,11 +24,11 @@ OPTIONS
 --dsos=::
 	Only consider symbols in these dsos. CSV that understands
 	file://filename entries.
--n
---show-nr-samples
+-n::
+--show-nr-samples::
 	Show the number of samples for each symbol
--T
---threads
+-T::
+--threads::
 	Show per-thread event counters
 -C::
 --comms=::