Updated description.

Author: TIFitis

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

@@ -1662,7 +1662,7 @@ def DeclareMapperOp : OpenMP_Op<"declare_mapper", traits = [
   let summary = "declare mapper directive";
   let description = [{
     The declare mapper directive declares a user-defined mapper for a given
-    type, and may define a mapper-identifier that can be used in a map clause.
+    type, and defines a mapper-identifier that can be used in a map clause.
   }] # clausesDescription;
 
   let arguments = !con((ins SymbolNameAttr:$sym_name,