video: msm: wfd: initialize mdp_iommu_split_domain for wfd

Initialize mdp_iommu_split_domain for both wfd devices. Without this
change, mdp_iommu_split_domain is uninitialized for the second wfd
device during secure session.

Change-Id: I82db1325110bef92a0bdd6832ca41f2cb258f0fa
CRs-fixed: 380161
Signed-off-by: Arun Menon <menon@codeaurora.org>