drm/mgag200: Set PCI option register in G200SE models

The initial value of the PCI option register got lost while refactoring
the driver init code. Restore the setting.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reported-by: kernel test robot <lkp@intel.com>
Fixes: 2021708e ("drm/mgag200: Initialize PCI registers early during device setup")
Cc: Lyude Paul <lyude@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Emil Velikov <emil.velikov@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200804065158.21049-1-tzimmermann@suse.de