finalize_branch_for_release.sh rel to root

Bug: 228979367
Test: run script from root
Change-Id: I0a5cfd4873ccf49fd53be745d61005e821bfa80d
diff --git a/finalize_branch_for_release.sh b/finalize_branch_for_release.sh
index d498beb..75381e3 100755
--- a/finalize_branch_for_release.sh
+++ b/finalize_branch_for_release.sh
@@ -2,7 +2,7 @@
 
 set -e
 
-source ../envsetup.sh
+source "$(dirname "$0")"/envsetup.sh
 
 # default target to modify tree and build SDK
 lunch aosp_arm64-userdebug