Fix bug in "maxDepth" logic

The method:
-(NSArray*)subviewsPassingTest:(BOOL(^)(UIView *subview, BOOL *stop))test
                      maxDepth:(NSInteger)maxDepth

.. contained an error in the logic for calculating "maxDepth" when
traversing up the UIView chain.  It was not checking to see if it had
traversed up to `self`, and was instead checking to see if it had
reached the root view.