[WebAssembly][NFC] Fix up SIMD bitwise tests

Summary:
The updated tests were previously infallible because the SIMD bitwise
operations do not contain vector types in their names.

Reviewers: aheejin, dschuff

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D51369

llvm-svn: 340858