[ONNX] Simplify Onnx.MatMulInteger op lowering (llvm#4163)

This commit modifies the Onnx.MatMulInteger op lowering to fix the
Torch->Linalg lowering path of the op.

Fixes nod-ai/SHARK-ModelDev#906.

Signed-off-by: Vivek Khandelwal <vivekkhandelwal1424@gmail.com>

Author: vivekkhandelwal1