cleanup a fix and add the vma_set_file function

["Christian König" <ckoenig.leichtzumerken@xxxxxxxxx>]

Hi Andrew,

can I get you Acked-by to merge this cleanup through the drm-misc-next branch? The affected drivers are mostly from the DRM subsystem.

The fix for the other problem you pointed out in mmap_region() has already shown up in that branch.

Thanks in advance,
Christian.