Mark 'tidss_pm_ops' as __maybe_unused to avoid
the warning: unused variable 'tidss_pm_ops'

Fixes: 6e120594 ("drm/tidss: Make use of the helper macro SET_RUNTIME_PM_OPS()")
Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211129063347.404-1-caihuoqing@baidu.com