tracing: Fix a comment and a trivial format issue in tracepoint.h

Fix the tracepoint documentation path in tracepoints headers and
a misaligned tabulation.

Signed-off-by: Li Hong <lihong.hi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
LKML-Reference: <3a3680030909220300h7cf18849q4d4702b9d4feaa67@mail.gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>