OvmfPkg: QemuBootOrder: initialize IsFinal variable to make MSVC happy

The BOOLEAN IsFinal variable initialization isn't properly seen by
MSVC. To make it compile OVMF the variable needs to be initialized.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Mauro Faccenda <faccenda@gmail.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15214 6f19259b-4bc3-4df7-8a09-765794883524