drm/gma500: Remove empty preclose hook

I'm auditing them all, empty ones just confuse ...

Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452548477-15905-9-git-send-email-daniel.vetter@ffwll.ch


Acked-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>