[arc] Fix ambiguous overloaded operator error

lib/Target/ARC/ARCISelLowering.cpp:490:22: error: use of overloaded operator '<<' is ambiguous (with operand types 'llvm::raw_ostream' and 'llvm::MVT::SimpleValueType')
                     << RegVT.getSimpleVT().SimpleTy << "\n");
                     ^  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

llvm-svn: 318443