Build prefix on pi-platform-release is PPRL.

BUG: 117431430
diff --git a/core/build_id.mk b/core/build_id.mk
index 7723647..6175b9a 100644
--- a/core/build_id.mk
+++ b/core/build_id.mk
@@ -18,4 +18,4 @@
 # (like "CRB01").  It must be a single word, and is
 # capitalized by convention.
 
-export BUILD_ID=PPR1.181005.003
+export BUILD_ID=PPRL.181005.003