drm/ast: Fail if connector initialization fails

Update the connector code to fail if the connector could not be
initialized. The current code just ignored the error and failed
later when the connector was supposed to be used.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220207141544.30015-2-tzimmermann@suse.de