Recommit r322073: [AArch64][SVE] Asm: Add predicated ADD/SUB instructions

Fixed issue that was found on sanitizer-x86_64-linux-fast.
I changed the result type of 'Parser.getTok().getString().lower()'
in AArch64AsmParser::tryParseSVEPredicateVector() from 'StringRef' to
'auto', since StringRef::lower() returns a std::string.

llvm-svn: 322092