drm: writeback: Add missing cleanup in case of initialization failure

The current implementation of drm_writeback_connector initialization does
not properly clean up all resources in case of failure (allocated
properties and possible_encoders). Add this cleaning in case of failure.

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20250116-google-vkms-managed-v9-6-3e4ae1bd05a0@bootlin.com


Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>