drm/panel: s6d7aa0: remove the unneeded variable in s6d7aa0_lock

Remove unneeded variable and directly return 0.

Signed-off-by: Wang Jianzheng <wangjianzheng@vivo.com>
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Artur Weber <aweber.kernel@gmail.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230608033446.18412-1-wangjianzheng@vivo.com