Don't Run ASSIGN on Every Report Step

Commit 5a060910a distinguished ASSIGN from DEFINE at the field
level, but did not make the same distinction at the well or group
levels.  Passing 'report_step' instead of assign.report_step() as an
argument to UDQState::assign() means we'd be running every ASSIGN
operation on every report step which would reset the state.  That's
a bug if the model defines some sort of cumulative UDQ at the well
or group levels.

src/opm/input/eclipse/Schedule/UDQ/UDQConfig.cpp

@@ -449,14 +449,14 @@ namespace Opm {
         const auto groups = sched.groupNames(report_step);
 
         for (const auto& assign : this->assignments(UDQVarType::WELL_VAR)) {
-            if (udq_state.assign(report_step, assign.keyword())) {
+            if (udq_state.assign(assign.report_step(), assign.keyword())) {
                 auto ws = assign.eval(wells);
                 context.update_assign(report_step, assign.keyword(), ws);
             }
         }
 
         for (const auto& assign : this->assignments(UDQVarType::GROUP_VAR)) {
-            if (udq_state.assign(report_step, assign.keyword())) {
+            if (udq_state.assign(assign.report_step(), assign.keyword())) {
                 auto ws = assign.eval(groups);
                 context.update_assign(report_step, assign.keyword(), ws);
             }