drm/rockchip: analogix_dp: Remove unused check and variables

Remove unused check and variables after:
drm/rockchip: Set line flag config register in vop_crtc_enable

Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1493469547-2121-1-git-send-email-jeffy.chen@rock-chips.com