[WebAssembly] MC: Fix value of R_WEBASSEMBLY_TABLE_INDEX relocations

Previously we were writing the value function index space
value but for these types of relocations we want to be
writing the table element index space value.

Add a test case for these relocation types that fails
without this change.

Differential Revision: https://reviews.llvm.org/D33962

llvm-svn: 305253