drm/i2c: tda998x: Fix memory leak in tda998x_encoder_init error path.

Commit 6ae668cc (drm/i2c: tda998x: check the CEC device creation)
introduced a memory leak in the error path of tda998x_encoder_init

Picked up by the nightly Coverity scan. CID 1174076

Signed-off-by: Dave Jones <davej@fedoraproject.org>
Acked-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>