drm: call drm_gem_object_funcs.mmap with fake offset

The fake offset is going to stay, so change the calling convention for
drm_gem_object_funcs.mmap to include the fake offset.  Update all users
accordingly.

Note that this reverts 83b8a6f242ea ("drm/gem: Fix mmap fake offset
handling for drm_gem_object_funcs.mmap") and on top then adds the fake
offset to  drm_gem_prime_mmap to make sure all paths leading to
obj->funcs->mmap are consistent.

v3: move fake-offset tweak in drm_gem_prime_mmap() so we have this code
    only once in the function (Rob Herring).

Fixes: 83b8a6f242ea ("drm/gem: Fix mmap fake offset handling for drm_gem_object_funcs.mmap")
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20191127092523.5620-2-kraxel@redhat.com
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 97a4816..0b37506 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -159,9 +159,7 @@ struct drm_gem_object_funcs {
 	 *
 	 * The callback is used by by both drm_gem_mmap_obj() and
 	 * drm_gem_prime_mmap().  When @mmap is present @vm_ops is not
-	 * used, the @mmap callback must set vma->vm_ops instead. The @mmap
-	 * callback is always called with a 0 offset. The caller will remove
-	 * the fake offset as necessary.
+	 * used, the @mmap callback must set vma->vm_ops instead.
 	 */
 	int (*mmap)(struct drm_gem_object *obj, struct vm_area_struct *vma);