tracing: Restore the const qualifier for field names and types definition

Restore the const qualifier in field's name and type parameters of
trace_define_field that was lost while solving a conflict.

Fields names and types are defined as builtin constant strings in
static TRACE_EVENTs. But kprobes allocates these dynamically.

That said, we still want to always pass these strings as const char *
in trace_define_fields() to avoid any further accidental writes on
the pointed strings.

Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 8079bb5..197cdaa 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -27,8 +27,8 @@
 
 LIST_HEAD(ftrace_events);
 
-int trace_define_field(struct ftrace_event_call *call, char *type,
-		       char *name, int offset, int size, int is_signed,
+int trace_define_field(struct ftrace_event_call *call, const char *type,
+		       const char *name, int offset, int size, int is_signed,
 		       int filter_type)
 {
 	struct ftrace_event_field *field;