[AT-SPI] fix a crash on scroll-view

[AT-SPI] fix a crash on scroll-view

This patch is resolving the crash with following stack.

__cxa_throw () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
Dali::Toolkit::Internal::ScrollView::ScrollTo
Dali::Toolkit::ScrollView::ScrollTo
Dali::Toolkit::Internal::ScrollView::AccessibleImpl::ScrollToChild
Dali::Toolkit::DevelControl::ControlAccessible::ScrollToSelf
Dali::Toolkit::DevelControl::ControlAccessible::GrabHighlight
Dali::Toolkit::DevelControl::GrabAccessibilityHighlight
Dali::Toolkit::Internal::AccessibilityManager::SetCurrentFocusActor
Dali::Toolkit::AccessibilityManager::SetCurrentFocusActor

It is not able to call ScrollView::ScrollTo,
if parent of child in ScrollTo is not the scrollView.

But the ControlAccessible can call ScrollTo when the parent can be
one of child's parents(ancestor).

Change-Id: Ie88c652f8a1ca348f6b8cbe9f95484a5eb5bf508