Change _book.yaml path for Tradefed generated docs.

Bug: 79989330

Test: Results staged at go/sac-staging/reference/tradefed

Change-Id: Ia47bc08939a8f6965bbb2bccb50173924f98a330
diff --git a/Android.mk b/Android.mk
index 4bcaeb6..a5b52c7 100644
--- a/Android.mk
+++ b/Android.mk
@@ -92,7 +92,7 @@
         -hdf android.whichdoc online \
         -hdf css.path /reference/assets/css/doclava-devsite.css \
         -hdf book.root toc \
-        -hdf book.path /reference/tradefed/_book.yaml \
+        -hdf book.path /_book.yaml \
         -yaml _book.yaml \
         -apidocsdir reference/tradefed/ \
         -werror \