[mlir][tosa] Get quantized element type with sign info. (#169387)
As mentioned in
https://github.com/llvm/llvm-project/blob/a27bb38ee6f5762e715803d8eb6ffc5a8dd09575/mlir/include/mlir/Dialect/Quant/IR/QuantTypes.h#L109
`QuantType::getStorageType` doesn't capture the sign information. This
lead to the following IR to fail during verification:
```
func.func @clamp(%arg0:tensor<?x112x112x32x!quant.uniform<u8:f32, 0.023529412224888802:-128>>) -> (tensor<?x112x112x32x!quant.uniform<u8:f32, 0.023529412224888802:-128>>) {
%0 = tosa.clamp %arg0 {max_val = 255 : ui8, min_val = 0 : ui8} : (tensor<?x112x112x32x!quant.uniform<u8:f32, 0.023529412224888802:-128>>) -> tensor<?x112x112x32x!quant.uniform<u8:f32, 0.023529412224888802:-128>>
return %0 : tensor<?x112x112x32x!quant.uniform<u8:f32, 0.023529412224888802:-128>>
}
```
with `'tosa.clamp' op min/max attributes types are incompatible with
input/output element types` error
since `getStorageType` was returning signed integer but the clamp
attributes were unsigned.
This PR updates the usage of `getStorageType` in tosa codebase to
correctly use the signed info for the quantized type.
