mm-video: venc: always align buffer before ion_map_iommu

Align buffer even if video dimensions are not multiple of 16. Video
encoder memory allocator allocates aligned memory in
venc_allocate_recon_buffers and pmem_allocate which will be mismatched
on multiple of 16 dimension video.

Change-Id: Ib88dd37a2526dffa5287b4153d5d7bc8b366d0f2