drm/rockchip: dw_hdmi: Use devm_regulator_get_enable()

The regulators are only enabled at bind() and disabled at unbind(),
hence replace the boilerplate code by making use of
devm_regulator_get_enable() helper.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240813-dw-hdmi-rockchip-cleanup-v1-3-b3e73b5f4fd6@collabora.com