[OpenMP][mlir] fix broken build

[peixin]

Thanks for fix this. Sorry to bother you.

mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td

let extraClassDeclaration = [{
     unsigned getNumVariableOperands() {
       assert(x() && "expected 'x' operand");
       assert(v() && "expected 'v' operand");
       return 2;
     }
 
     /// The i-th variable operand passed.
     Value getVariableOperand(unsigned i) {
-      assert(0 <= i < 2 && "invalid index position for an operand");
+      assert(0 <= i && i < 2 && "invalid index position for an operand");
       return i == 0 ? x() : v();
     }
   }];
 }
 
 def AtomicWriteOp : OpenMP_Op<"atomic.write"> {
 
   let summary = "performs an atomic write";
let extraClassDeclaration = [{
     unsigned getNumVariableOperands() {
       assert(address() && "expected address operand");
       assert(value() && "expected value operand");
       return 2;
     }
 
     /// The i-th variable operand passed.
     Value getVariableOperand(unsigned i) {
-      assert(0 <= i < 2 && "invalid index position for an operand");
+      assert(0 <= i && i < 2 && "invalid index position for an operand");
       return i == 0 ? address() : value();
     }
   }];
 }
 
 def AtomicUpdateOp : OpenMP_Op<"atomic.update",
                                [SingleBlockImplicitTerminator<"YieldOp">]> {
 

mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp

if (failed(converter->convertTypes(curOp->getResultTypes(), resTypes)))
       return failure();
     SmallVector<Value> convertedOperands;
     for (unsigned idx = 0; idx < curOp.getNumVariableOperands(); ++idx) {
       Value originalVariableOperand = curOp.getVariableOperand(idx);
       if (!originalVariableOperand)
         return failure();
       if (originalVariableOperand.getType().isa<MemRefType>()) {
         // TODO: Support memref type in variable operands
-        rewriter.notifyMatchFailure(curOp, "memref is not supported yet");
+        return rewriter.notifyMatchFailure(curOp,
+                                           "memref is not supported yet");
       } else {
         convertedOperands.emplace_back(adaptor.getOperands()[idx]);
       }
     }
     rewriter.replaceOpWithNewOp<T>(curOp, resTypes, convertedOperands,
                                    curOp->getAttrs());
     return success();
   }