Bug fix for getConstantBoundOnDimSize

- this was detected when memref-bound-check was run on the output of the
  loop-fusion pass
- the addition (to represent ceildiv as a floordiv) had to be performed only
  for the constant term of the constraint
- update test cases
- memref-bound-check no longer returns an error on the output of this test case

PiperOrigin-RevId: 236731137