tracing: Fix missing * in comment block

There is a missing * in a comment block, add it in.

Link: https://lkml.kernel.org/r/20211006172830.1025336-1-colin.king@canonical.com

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_hist.c

@@ -2506,7 +2506,7 @@ find_synthetic_field_var(struct hist_trigger_data *target_hist_data,
  * events.  However, for convenience, users are allowed to directly
  * specify an event field in an action, which will be automatically
  * converted into a variable on their behalf.
-
+ *
  * If a user specifies a field on an event that isn't the event the
  * histogram currently being defined (the target event histogram), the
  * only way that can be accomplished is if a new hist trigger is