[OMPIRBuilder] Fix use of uninitialized variable. (#145883)
The code in `OpenMPIRBuilder::getTargetEntryUniqueInfo` calls
`ID.getDevice()` even when `getUniqueID` has failed and ID is
un-initialized. This caused a sanitizer fail for me in
https://github.com/llvm/llvm-project/pull/145026. Fix it by giving a
default value to `ID`. The value chosen is the same as used in
`OpenMPToLLVMIRTranslation.cpp`.