Fixes BHV-15492

## Issue
Call to setLastFocusedChild in Scroller.scrollToControl assumes that the this.$.viewport is the spotlight container and as such is telling it to remember which control was scrolled to.

## Fix
Configuring last focused child on scroller because it is now the spotlight container.

Enyo-DCO-1.1-Signed-off-by: Ryan Duffy (ryan.duffy@lge.com)