OvmfPkg/QemuVideoDxe: use child handle to open parent protocols

Reorder when the child handle is created so that a parent / child relationship is established when PciIo protocol is opened.
This resolves some issues with code which depends on the parent/child relationship to locate the GOP protocol.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Chris Ruffin <cmruffin@gmail.com)