drm/i915: remove unused has_dma_mapping flag

After the previous patch this flag will check always clear, as it's
never set for shmem backed and userptr objects, so we can remove it.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Yeah this isn't really fixes but it's a nice cleanup to
clarify the code but not really worth the hassle of backmerging. So
just add to -fixes, we're still early in -rc.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -213,7 +213,6 @@ i915_gem_object_get_pages_phys(struct drm_i915_gem_object *obj)
 	sg_dma_len(sg) = obj->base.size;
 
 	obj->pages = st;
-	obj->has_dma_mapping = true;
 	return 0;
 }
 
@@ -265,8 +264,6 @@ i915_gem_object_put_pages_phys(struct drm_i915_gem_object *obj)
 
 	sg_free_table(obj->pages);
 	kfree(obj->pages);
-
-	obj->has_dma_mapping = false;
 }
 
 static void