Simplify ff prepared rounding check.

Signed-off-by: Finn Carroll <[email protected]>

server/src/main/java/org/opensearch/search/aggregations/bucket/histogram/AutoDateHistogramAggregator.java

@@ -202,8 +202,7 @@ protected Rounding getRounding(final long low, final long high) {
                 }
 
                 // Ensure preparedRounding never shrinks
-                roundingIdx = Math.max(prevRoundingIdx, roundingIdx);
-                if (roundingIdx != prevRoundingIdx) {
+                if (roundingIdx > prevRoundingIdx) {
                     preparedRounding = prepareRounding(roundingIdx);
                 }