[MLIR][Affine] Fix createPrivateMemRef in affine fusion

Always define a remapping for the memref replacement (`indexRemap`)
with the proper number of inputs, including all the `outerIVs`, so that
the number of inputs and the operands provided for the map don't mismatch.

Reviewed By: bondhugula, andydavis1

Differential Revision: https://reviews.llvm.org/D85177