Implement data pointer clang-tidy check

readability-container-data-pointer flags one error in our codebase, but
can definitely find issues in patchsets.  Fix the one error (that came
from crow), and enable the check.

Change-Id: I3045ec9a58d80300c90921dda1a2fe3859ffed7b
Signed-off-by: Ed Tanous <edtanous@google.com>
diff --git a/.clang-tidy b/.clang-tidy
index 32f7f75..308c3f9 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -280,6 +280,7 @@
 readability-avoid-const-params-in-decls,
 readability-braces-around-statements,
 readability-const-return-type,
+readability-container-data-pointer,
 readability-container-size-empty,
 readability-convert-member-functions-to-static,
 readability-delete-null-pointer,