msm_fb: display: do not use ION_IOMMU_UNMAP_DELAYED

Since iommu buffers will be unmapped after two newer commits
had passed, there is no need to request iommu driver to further
delay unmapping an iommu buffer.

Change-Id: I8cf8d406cf509908035d12c9a04f0add12f3c7c7
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>