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>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/OvmfPkg@14987 6f19259b-4bc3-4df7-8a09-765794883524