[NFC] Add { } to silence compiler warning [-Wmissing-braces].

../llvm-project/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp:355:48: warning: suggest braces around initialization of subobject [-Wmissing-braces]
      return addMappingFromTable<1>(MI, MRI, { 0 }, Table);
                                               ^
                                               {}

llvm-svn: 373784