fix property name "microdroid_manager.apk_root_hash"

Bug: 193504400
Test: second run of microdroid should show
  "Saved root_hash is verified"
Change-Id: I604439c5642fb66ae2b3a465b9dd416284f341ca
diff --git a/apkdmverity/src/main.rs b/apkdmverity/src/main.rs
index 2cc0758..cabeb35 100644
--- a/apkdmverity/src/main.rs
+++ b/apkdmverity/src/main.rs
@@ -62,7 +62,7 @@
     let apk = matches.value_of("apk").unwrap();
     let idsig = matches.value_of("idsig").unwrap();
     let name = matches.value_of("name").unwrap();
-    let roothash = if let Ok(val) = system_properties::read("microdroid_manager.apk_roothash") {
+    let roothash = if let Ok(val) = system_properties::read("microdroid_manager.apk_root_hash") {
         Some(util::parse_hexstring(&val)?)
     } else {
         // This failure is not an error. We will use the roothash read from the idsig file.