[llvm] [yaml2obj] Don't use uninitialized Type (PR #123274)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

@jh7370 I don't this is significantly different https://github.com/llvm/llvm-project/pull/123137 
I don't see the bug you described, TypeStr is not empty.

And we can't bailout on error(), as without `default:` it crashes on other assertions.

For reference, this is existing llvm-project/llvm/test/tools/yaml2obj/ELF/mips-abi-flags.yaml


https://github.com/llvm/llvm-project/pull/123274