packages: use chroot-relative path for DriveFS

BUG=chromium:1118212
TEST=pending

Change-Id: Ib13a10b5939358951f89234588cf66fa992ae8fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2507297
Tested-by: Jose Magana <jomag@chromium.org>
Commit-Queue: Jose Magana <jomag@chromium.org>
Reviewed-by: Jose Magana <jomag@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Auto-Submit: Jose Magana <jomag@chromium.org>
diff --git a/service/packages.py b/service/packages.py
index 0448420..994f6bc 100644
--- a/service/packages.py
+++ b/service/packages.py
@@ -311,7 +311,7 @@
 
   result = uprev_lib.UprevVersionedPackageResult()
 
-  pkg_path = os.path.join(constants.SOURCE_ROOT, DRIVEFS_PATH, 'drivefs')
+  pkg_path = os.path.join(DRIVEFS_PATH, 'drivefs')
 
   uprev_result = uprev_lib.uprev_workon_ebuild_to_version(pkg_path,
                                                           target_version,
@@ -323,7 +323,7 @@
 
   all_changed_files.extend(uprev_result.changed_files)
 
-  pkg_path = os.path.join(constants.SOURCE_ROOT, DRIVEFS_PATH, 'drivefs-ipc')
+  pkg_path = os.path.join(DRIVEFS_PATH, 'drivefs-ipc')
 
   uprev_result = uprev_lib.uprev_workon_ebuild_to_version(pkg_path,
                                                           target_version,