tracing/kprobe: Fix uninitialized variable bug

There is a potential execution path in which variable *ret* is returned
without being properly initialized, previously.

Fix this by initializing variable *ret* to 0.

Link: http://lkml.kernel.org/r/20200205223404.GA3379@embeddedor

Addresses-Coverity-ID: 1491142 ("Uninitialized scalar variable")
Fixes: 2a588dd1 ("tracing: Add kprobe event command generation functions")
Reviewed-by: NTom Zanussi <zanussi@kernel.org>
Acked-by: NMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: NGustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_kprobe.c

@@ -1012,7 +1012,7 @@ int __kprobe_event_add_fields(struct dynevent_cmd *cmd, ...)
 {
 	struct dynevent_arg arg;
 	va_list args;
-	int ret;
+	int ret = 0;
 
 	if (cmd->type != DYNEVENT_TYPE_KPROBE)
 		return -EINVAL;