drm/hisilicon: Delete the unused macro

The macro PADDING is no longer used. Delete it.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1601340326-14049-1-git-send-email-tiantao6@hisilicon.com