iommu: msm: Fix potential memory leak in unmapping

A memory leak can occur when we have a 2MB mapping
followed by smaller mappings requiring 3rd level page
tables. Fix this potential for memory leak in iommu
unmapping code for LPAE by not assuming that the next
entry after a 2MB mapping is also a 2MB mapping.

CRs-fixed: 659056
Change-Id: I51f5bf2feedc6460adccbfb17070331b7c28454f
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>