wm8350-regulator: fix wm8350_register_regulator error handling

In the case of platform_device_add() fail, we should call
platform_device_put() instead of platform_device_del()

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>