[DebugInfo] Attempt to fix regression test failure after 59a76d95

Test case `test/CodeGen/WebAssembly/stackified-debug.ll`
was failing due to malformed DwarfExpression.

This failure has been seen in lot of bots, for instance in:
http://lab.llvm.org:8011/builders/lld-x86_64-ubuntu-fast/builds/18794

: 'RUN: at line 1'
/home/buildbot/as-builder-4/lld-x86_64-ubuntu-fast/build/bin/llc
/home/buildbot/as-builder-4/lld-x86_64-ubuntu-fast/build/bin/FileCheck /home/buildbot/as-builder-4/lld-x86_64-ubuntu-fast/llvm-project/llvm/test/CodeGen/WebAssembly/stackified-debug.ll
home/buildbot/as-builder-4/lld-x86_64-ubuntu-fast/llvm-project/llvm/test/CodeGen/WebAssembly/stackified-debug.ll:26:10: error: CHECK: expected string not found in input
 CHECK: .int16 4 # Loc expr size
         ^
<stdin>:34:2: note: scanning from here
 .int16 3 # Loc expr size

Differential Revision: https://reviews.llvm.org/D83560