[mlir][LLVMIR] Fix fusion for rank-0 tensors

Summary: This diff fixes fusion craching for ops with rank-0 tensors

Reviewers: mravishankar, nicolasvasilache, rriddle!

Subscribers: mehdi_amini, rriddle, jpienaar, burmako, shauheen, antiagainst, arpith-jacob, mgester, lucyrfox, liufengdb, Joonsoo, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76479