Be more C++. volume UUID should always be std::string.

Test: boots
Bug: 67041047
Change-Id: I36d3944ae8de192703b9ee359900841b833fe3a1
diff --git a/Utils.h b/Utils.h
index 4e2be96..8d09ddf 100644
--- a/Utils.h
+++ b/Utils.h
@@ -103,10 +103,10 @@
 std::string BuildDataMiscDePath(userid_t userid);
 std::string BuildDataProfilesDePath(userid_t userid);
 
-std::string BuildDataPath(const char* volumeUuid);
-std::string BuildDataMediaCePath(const char* volumeUuid, userid_t userid);
-std::string BuildDataUserCePath(const char* volumeUuid, userid_t userid);
-std::string BuildDataUserDePath(const char* volumeUuid, userid_t userid);
+std::string BuildDataPath(const std::string& volumeUuid);
+std::string BuildDataMediaCePath(const std::string& volumeUuid, userid_t userid);
+std::string BuildDataUserCePath(const std::string& volumeUuid, userid_t userid);
+std::string BuildDataUserDePath(const std::string& volumeUuid, userid_t userid);
 
 dev_t GetDevice(const std::string& path);