drm/i2c: tda998x: unregister the connector in the unbind function

tda998x uses drm_connector_register() in the .bind function that
needs to be balanced with a drm_connector_unregister() in the .unbind.
Otherwise dangling sysfs entries are left behind and future rebinds
will fail.

Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>