linux-phytec-fsl

drm/i915: Protect private gem objects from truncate (such as imported dmabuf)

If the object has no backing shmemfs filp, then we obviously cannot
perform a truncation operation upon it.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>