tracing: Make trace_define_field_ext() static

trace_define_field_ext() is not used outside of trace_events.c, it should
be static.

Link: https://lore.kernel.org/oe-kbuild-all/202302130750.679RaRog-lkp@intel.com/

Fixes: b6c7abd1 ("tracing: Fix TASK_COMM_LEN in trace event format file")
Reported-by: Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/trace_events.c

@@ -155,7 +155,7 @@ int trace_define_field(struct trace_event_call *call, const char *type,
 }
 EXPORT_SYMBOL_GPL(trace_define_field);
 
-int trace_define_field_ext(struct trace_event_call *call, const char *type,
+static int trace_define_field_ext(struct trace_event_call *call, const char *type,
 		       const char *name, int offset, int size, int is_signed,
 		       int filter_type, int len)
 {