configs: fix CHI config for Garnet

CHI.py was not working with Garnet as ruby_system.network.buffer_size
only exists in SimpleNetwork.

Change-Id: I00e952f8881d385e3591c149e08c9c7a53fda2cd
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63811
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/configs/ruby/CHI.py b/configs/ruby/CHI.py
index d31d233..df97b92 100644
--- a/configs/ruby/CHI.py
+++ b/configs/ruby/CHI.py
@@ -266,7 +266,8 @@
 
     ruby_system.network.control_msg_size = params.cntrl_msg_size
     ruby_system.network.data_msg_size = params.data_width
-    ruby_system.network.buffer_size = params.router_buffer_size
+    if options.network == "simple":
+        ruby_system.network.buffer_size = params.router_buffer_size
 
     # Incorporate the params into options so it's propagated to
     # makeTopology and create_topology the parent scripts