regulator: ab8500 - fix the logic to remove already registered regulators in error path

In current implementation, ab8500_regulator_info[0].regulator is not
unregistered if the error happen at i > 0.

This patch fixes the resource leak and also improves the readability.

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