tpm-tools: fix build failures caused by -Werror

This fixes this build failure (and many others):
  http://autobuild.buildroot.org/results/d56/d56bfc69ef0a478219c959d50fb96d526fc2155e/



The build failure is caused by the build system using -Werror; this is
already patched upstream, so this commit just imports the upstream
patch.

Signed-off-by: Noé Rubinstein <noe.rubinstein@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>