regulator: simplify regulator_register() error handling

Simply remove all consumer supplies for the regulator on errors. Remove
unset_consumer_device_supply() which is no longer used.

Signed-off-by: Jani Nikula <ext-jani.1.nikula@nokia.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>