fix superproject definition: include revision

repo changed the default handling for superproject. It no longer
considers the containing branch name, but rather the default revision.
Mitigate that by explicitly setting the revision in the superproject
tag.

Bug: 181627166
Bug: 206514481
Signed-off-by: Matthias Maennich <maennich@google.com>
Change-Id: I7645927e1b477a0fb1b70fd51a279da9c84a862e
diff --git a/default.xml b/default.xml
index 6dd2dc3..2ee6569 100644
--- a/default.xml
+++ b/default.xml
@@ -3,7 +3,7 @@
   <remote  name="aosp" fetch=".." review="https://android-review.googlesource.com/" />
   <default revision="master" remote="aosp" sync-j="4" />
 
-  <superproject name="kernel/superproject" remote="aosp"/>
+  <superproject name="kernel/superproject" remote="aosp" revision="common-android-mainline" />
 
   <project path="build/kernel" name="kernel/build" >
     <linkfile src="kleaf/bazel.sh" dest="tools/bazel" />