objtool: Use value of intended enum to compile with clang

[Lukas Bulwahn]

Hi,

Please include this patch in tools/objtool to properly compile with clang-5.0.

I successfully compiled this patch (make defconfig && make) on top of tag
next-20171208 from linux-next with clang-5.0.0 and gcc (Debian 7.2.0-16) 7.2.0,
but I did not test anything further than that.

Exact compiler version of clang-5.0.0 is:

  clang version 5.0.0-+rc2-1 (tags/RELEASE_500/rc2)
  Target: x86_64-pc-linux-gnu
  Thread model: posix
  InstalledDir: /usr/bin

This is my first kernel contribution, so please apologize any kernel newbie
mistakes.

Lukas