Small fix: Use const value on IsHashreeDisabled

Bug: N/A
Test: Presubmit
Change-Id: I2167ac6d022c2c8c96febf2fc82eb3bba6fb6541
diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index b5292a4..c0b9281 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -732,7 +732,7 @@
     return true;
 }
 
-bool IsHashtreeDisabled(const AvbHandle& vbmeta, std::string mount_point) {
+bool IsHashtreeDisabled(const AvbHandle& vbmeta, const std::string& mount_point) {
     if (vbmeta.status() == AvbHandleStatus::kHashtreeDisabled ||
         vbmeta.status() == AvbHandleStatus::kVerificationDisabled) {
         LOG(ERROR) << "Top-level vbmeta is disabled, skip Hashtree setup for " << mount_point;