[MLIR] NFC. Make affine analysis utils method const correct

Make isSliceValid const correct. NFC.

Author: bondhugula

mlir/include/mlir/Dialect/Affine/Analysis/Utils.h

@@ -312,7 +312,7 @@ struct ComputationSliceState {
   /// return false as it implies that the effective fusion results in at least
   /// one iteration of the slice that was not originally in the source's domain.
   /// If the validity cannot be determined, returns std::nullopt.
-  std::optional<bool> isSliceValid();
+  std::optional<bool> isSliceValid() const;
 
   void dump() const;
 

mlir/lib/Dialect/Affine/Analysis/Utils.cpp

@@ -687,7 +687,7 @@ std::optional<bool> ComputationSliceState::isSliceMaximalFastCheck() const {
 /// Returns true if it is deterministically verified that the original iteration
 /// space of the slice is contained within the new iteration space that is
 /// created after fusing 'this' slice into its destination.
-std::optional<bool> ComputationSliceState::isSliceValid() {
+std::optional<bool> ComputationSliceState::isSliceValid() const {
   // Fast check to determine if the slice is valid. If the following conditions
   // are verified to be true, slice is declared valid by the fast check:
   // 1. Each slice loop is a single iteration loop bound in terms of a single