Fix warnings: Possible accidental assignment in place of a comparison. A condition expression should not be reduced to an assignment

Eclipse Version 2022-06 (4.24.0) reports this warning in the following places:

```
Possible accidental assignment in place of a comparison. A condition expression should not be reduced to an assignment PrEffectHelper.java line 168 /graphics/src/main/java/com/sun/scenario/effect/impl/prism
Possible accidental assignment in place of a comparison. A condition expression should not be reduced to an assignment StyleManager.java line 1275 /graphics/src/main/java/com/sun/javafx/css
Possible accidental assignment in place of a comparison. A condition expression should not be reduced to an assignment Utils.java line 875 /graphics/src/main/java/com/sun/javafx/util
```