drm/ast: Fail probing if DDC channel could not be initialized

Expect the hardware to provide a DDC channel. Fail probing if its
initialization fails. Failing to initialize the DDC indicates a
larger problem, so there's no point in continuing.

v4:
	* give a rational in the commit message

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-3-tzimmermann@suse.de