idmap2: fix clang-tidy warnings [readability-*]

Bug: 120024673
Test: mmm frameworks/base/cmds/idmap2; check output
Change-Id: I1565afac8d34e4347d8c946228d1134211e8b435
diff --git a/cmds/idmap2/tests/TestHelpers.h b/cmds/idmap2/tests/TestHelpers.h
index 18dc541..356db7a 100644
--- a/cmds/idmap2/tests/TestHelpers.h
+++ b/cmds/idmap2/tests/TestHelpers.h
@@ -117,7 +117,7 @@
 
 const unsigned int idmap_raw_data_len = 565;
 
-const std::string GetTestDataPath();
+std::string GetTestDataPath();
 
 class Idmap2Tests : public testing::Test {
  protected: