regulator: fix device_register() error handling

If device_register() fails then call put_device().
See comment to device_register.

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>