drm: bridge: it66121: Use devm_regulator_bulk_get_enable()

Simplify the code of the driver by using
devm_regulator_bulk_get_enable(), which will handle powering up the
regulators, and disabling them on probe error or module removal.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221214125821.12489-3-paul@crapouillou.net