If an encoder fails to initialize the device can still be used without
the failed encoder. Don't propagate the error out of the probe function
but just skip the failed encoder.

As a special case a deferred probe request from the encoder is still
propagated out of the probe function in order not to break the deferred
probing mechanism.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>