drm/mediatek: don't use drm_put_dev

drm/mediatek: don't use drm_put_dev

[ Upstream commit ae9d2daecf086958a41ad216152ec208d70ba325 ]

fsl is already fully demidlayered in the probe function, but for
convenience stuck with drm_put_dev. Call the unregister/unref parts
separately, to make sure this driver works correct.

Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: CK Hu <ck.hu@mediatek.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161208110739.24417-3-daniel.vetter@ffwll.ch
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>