roomservice: Do not overwrite existing devices

When roomservice encounters an existing device folder, do not attempt to
overwrite it.

A user might have their own (possibly forked) device repo and might not
want to sync the device from omni.

Dependencies of the device will still be fetched, just do not
"hard-code" that the device must come from omni's gerrit/github.

Signed-off-by: Felix <google@ix5.org>
Change-Id: Icbda42d99880d02afa39b44ca5bf508de8626ba5
diff --git a/build/tools/roomservice.py b/build/tools/roomservice.py
index 60fccd0..6e20d37 100755
--- a/build/tools/roomservice.py
+++ b/build/tools/roomservice.py
@@ -370,6 +370,7 @@
 def fetch_device(device):
     if check_device_exists(device):
         print("WARNING: Trying to fetch a device that's already there")
+        return
     git_data = search_gerrit_for_device(device)
     if git_data is not None:
         device_url = git_data['id']