drm: omapdrm: displays: panel-dsi-cm: Fix field access before set

The driver accesses the ddata->in field before it gets set in the
dsicm_connect() function. Use the local in pointer variable instead.

Fixes: 7877632b4cd0 ("drm: omapdrm: displays: Get panel source at connect time")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>