Fix parsing of hex-format index dense tensor attributes.

TensorLiteralParser::getHexAttr does a isIntOrIndexOrFloat check and properly handles index elements, but TensorLiteralParser::getAttr that calls into it has a mismatched check. This just makes the checks match so that index element attrs can parse when of type tensor.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D111374