drm/omap: fix uninitialized ret variable

drm/omap: fix uninitialized ret variable

audio_config function for both HDMI4 and HDMI5 return uninitialized
value as the error code if the display is not currently enabled. For
some reason this has not caused any issues.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180329104038.29154-1-tomi.valkeinen@ti.com
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>