m86k: adjust the usage of ArgInfo after change 9b057f647d70fc958d4a1a7a00e2deba65

Fails with:

```

/build/llvm-toolchain-snapshot-13~++20210709092633+88326bbc/llvm/lib/Target/M68k/GlSel/M68kCallLowering.cpp: In member function 'virtual bool llvm::M68kCallLowering::lowerReturn(llvm::MachineIRBuilder&, const llvm::Value*, llvm::ArrayRef<llvm::Register>, llvm::FunctionLoweringInfo&, llvm::Register) const':
/build/llvm-toolchain-snapshot-13~++20210709092633+88326bbc/llvm/lib/Target/M68k/GlSel/M68kCallLowering.cpp:71:42: error: no matching function for call to 'llvm::CallLowering::ArgInfo::ArgInfo(<brace-enclosed initializer list>)'
     ArgInfo OrigArg{VRegs, Val->getType()};
```

Differential Revision: https://reviews.llvm.org/D105689