drm/imx: tve: fix regulator_disable error path

Add missing regulator_disable() as devm_action to avoid dedicated
unbind() callback and fix the missing error handling.

Fixes: fcbc51e5 ("staging: drm/imx: Add support for Television Encoder (TVEv2)")
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>