Fix bug in sparse MDP reachability reward interval iteration

Due to a typo, the upper iteration uses `updateValueFromBelow` instead of `updateValueFromAbove`
to update the value vector. When the flag for monotonicity enforcement from above is active (default),
all values are thus forced to be above the upper bound, preventing convergence.

Example:
prism functionality/verify/mdps/reach/mdp_simple.nm functionality/verify/mdps/reach/mdp_simple.nm.props -sparse -intervaliter

+ test case

prism-tests/functionality/verify/mdps/reach/mdp_simple.nm.props.args

@@ -5,3 +5,8 @@
 -ex -gs
 -ex -politer
 -ex -modpoliter
+-s -ii
+-m -ii
+-h -ii
+-ex -valiter -ii
+-ex -gs -ii

prism/src/sparse/PS_NondetReachRewardInterval.cc

@@ -395,7 +395,7 @@ jint flags
 			}
 			// set vector element
 			// (if there were no choices from this state, reward is zero/infinity)
-			helper.updateValueFromBelow(soln_above2[i], soln_above[i], (h1 > l1) ? d1 : inf_vec[i] > 0 ? HUGE_VAL : 0);
+			helper.updateValueFromAbove(soln_above2[i], soln_above[i], (h1 > l1) ? d1 : inf_vec[i] > 0 ? HUGE_VAL : 0);
 		}
 
 		if (iterationExport) {