[mlir][NFC] Fix codestyle issues introduced in D121988

These were noticed in the post commit review of https://reviews.llvm.org/D121988

Author: zero9178

mlir/lib/Transforms/Utils/RegionUtils.cpp

@@ -533,7 +533,7 @@ LogicalResult BlockMergeCluster::addToCluster(BlockEquivalenceData &blockData) {
 
         if (!isValidSuccessorArg(leaderBlock, lhsOperand) ||
             !isValidSuccessorArg(mergeBlock, rhsOperand))
-          return mlir::failure();
+          return failure();
 
         mismatchedOperands.emplace_back(opI, operand);
         continue;

mlir/test/lib/Dialect/Test/TestDialect.cpp

@@ -348,9 +348,8 @@ TestBranchOp::getMutableSuccessorOperands(unsigned index) {
 Optional<MutableOperandRange>
 TestProducingBranchOp::getMutableSuccessorOperands(unsigned index) {
   assert(index <= 1 && "invalid successor index");
-  if (index == 1) {
+  if (index == 1)
     return getFirstOperandsMutable();
-  }
   return getSecondOperandsMutable();
 }