drm/rockchip: Fix build warning in analogix_dp-rockchip.c

I didn't catch this before applying, just right after (of course).

Fixes:
../drivers/gpu/drm/rockchip/analogix_dp-rockchip.c: In function
‘rockchip_dp_of_probe’:
../drivers/gpu/drm/rockchip/analogix_dp-rockchip.c:276:6: warning:
unused variable ‘ret’ [-Wunused-variable]
  int ret;
        ^~~

Fixes: 102712a3 ("drm/rockchip: analogix_dp: Remove unnecessary init
code")
Cc: Jeffy Chen <jeffy.chen@rock-chips.com>
Cc: Mark Yao <mark.yao@rock-chips.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-rockchip@lists.infradead.org
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20171020172557.54900-1-seanpaul@chromium.org