devlink: add value check to devlink_info_version_put()

Prevent from proceeding if there's nothing to print.

Suggested-by: Przemek Kitszel <[e-mail]>
Reviewed-by: Jiri Pirko <[e-mail]>
Reviewed-by: Kalesh AP <[e-mail]>
Tested-by: Bharath R <[e-mail]>
Signed-off-by: Jedrzej Jagielski <[e-mail]>
Signed-off-by: Tony Nguyen <[e-mail]>

net/devlink/dev.c

···
 		req->version_cb(version_name, version_type,
 				req->version_cb_priv);
 
-	if (!req->msg)
+	if (!req->msg || !*version_value)
 		return 0;
 
 	nest = nla_nest_start_noflag(req->msg, attr);