[WebAssembly] Fix stack offsets of return values from call lowering.

Summary: Fixes PR35220

Reviewers: vadimcn, alexcrichton

Reviewed By: alexcrichton

Subscribers: pepyakin, alexcrichton, jfb, dschuff, sbc100, jgravelle-google, llvm-commits, aheejin

Differential Revision: https://reviews.llvm.org/D39866

llvm-svn: 317895