[mlir][sparse][nfc] Fix memory leak in sparse sampled matmul integration test

[vmrajas]

Summary

https://reviews.llvm.org/D130023 added a memory leak in sparse_sampled_matmul.mlir
This diff fixes the memory leak.

Testing: Ran integration tests after building with -DLLVM_USE_SANITIZER=Address flag.

mlir/test/Integration/Dialect/SparseTensor/CPU/sparse_sampled_matmul.mlir

func.func @entry() {
     %c10 = arith.constant 10 : index
 
     // Setup memory for the dense matrices and initialize.
     %a0 = bufferization.alloc_tensor(%c5, %c10) : tensor<?x?xf32>
     %b0 = bufferization.alloc_tensor(%c10, %c5) : tensor<?x?xf32>
     %x0 = bufferization.alloc_tensor(%c5, %c5) : tensor<?x?xf32>
     %a, %b, %x = scf.for %i = %c0 to %c5 step %c1 iter_args(%a1 = %a0, %b1 = %b0, %x1 = %x0)
         -> (tensor<?x?xf32>, tensor<?x?xf32>, tensor<?x?xf32>) {
-      %x2 = scf.for %j = %c0 to %c5 step %c1 iter_args(%x3 = %x0) -> (tensor<?x?xf32>) {
+      %x2 = scf.for %j = %c0 to %c5 step %c1 iter_args(%x3 = %x1) -> (tensor<?x?xf32>) {
         %x4 = tensor.insert %d0 into %x3[%i, %j] : tensor<?x?xf32>
         scf.yield %x4 : tensor<?x?xf32>
       }
       %p = arith.addi %i, %c1 : index
       %q = arith.index_cast %p : index to i32
       %d = arith.sitofp %q : i32 to f32
       %a2, %b2 = scf.for %j = %c0 to %c10 step %c1 iter_args(%a3 = %a1, %b3 = %b1)
           -> (tensor<?x?xf32>, tensor<?x?xf32>) {