[Docs] Fix LangRef links referred in GetElementPtr.rst

Patch by chenwj!

Differential Revision: https://reviews.llvm.org/D32929


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303499 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed