drm/rockchip: cnd-dp: adjust spdif register setting

We use jitter bypass mode for spdif, so do not need to set jitter mode
related bit in SPDIF_CTRL_ADDR register. But of course we need to keep
the SPDIF_ENABLE bit.

Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Lin Huang <hl@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1526979222-32478-1-git-send-email-hl@rock-chips.com