tools: Fix gonk shutdown exception

Fixes serial connection cleanup errors.

Change-Id: I405d6cff28149218aea867da8e7f8ef1ea68d88d
Reviewed-on: https://pigweed-review.googlesource.com/c/gonk/+/242096
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Pigweed-Auto-Submit: Anthony DiGirolamo <tonymd@google.com>
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Akira Baruah <akirabaruah@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/tools/gonk_tools/gonk.py b/tools/gonk_tools/gonk.py
index 1934134..b72dad1 100644
--- a/tools/gonk_tools/gonk.py
+++ b/tools/gonk_tools/gonk.py
@@ -576,8 +576,9 @@
     try:
         miniterm.join(True)
     except KeyboardInterrupt:
-        pass
+        miniterm.stop()
     sys.stderr.write('\n--- exit ---\n')
+    miniterm.join()
     miniterm.close()
 
     return 0