OvmfPkg/QemuVideoDxe: child handles should have open parent protocol BY_CHILD_CONTROLLER

The QemuVideoDxe driver creates child controller handles, so it is acting
as a hybrid bus driver. The child handles should open the parent's bus
protocol BY_CHILD_CONTROLLER to properly maintain the protocol usage count.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Chris Ruffin <chris.ruffin@intel.com>