ext: Fix dumping stats error at the end of simulation

A missing comma causing two commands to be one, which resulted in
a Python interpreter syntax error.

Change-Id: Ieb0e3c620c175731084ff0e2040388b15364691e
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54343
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/ext/sst/gem5.cc b/ext/sst/gem5.cc
index 8eab6281..7af0eed 100644
--- a/ext/sst/gem5.cc
+++ b/ext/sst/gem5.cc
@@ -262,7 +262,7 @@
         // output gem5 stats
         const std::vector<std::string> output_stats_commands = {
-            "import m5.stats"
+            "import m5.stats",