Use correct macro for reltablespace.

It's an OID. WRITE_UINT_FIELD is identical to WRITE_OID_FIELD, but let's
be tidy.

Mark Dilger

src/backend/nodes/outfuncs.c

@@ -1784,7 +1784,7 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
 	WRITE_NODE_FIELD(cheapest_unique_path);
 	WRITE_NODE_FIELD(cheapest_parameterized_paths);
 	WRITE_UINT_FIELD(relid);
-	WRITE_UINT_FIELD(reltablespace);
+	WRITE_OID_FIELD(reltablespace);
 	WRITE_ENUM_FIELD(rtekind, RTEKind);
 	WRITE_INT_FIELD(min_attr);
 	WRITE_INT_FIELD(max_attr);