drm/tidss: Return error value from from softreset

Return an error value from dispc_softreset() so that the caller can
handle the errors.

Reviewed-by: Aradhya Bhatia <a-bhatia1@ti.com>
Link: https://lore.kernel.org/r/20231109-tidss-probe-v2-5-ac91b5ea35c0@ideasonboard.com


Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>