regulator: ab8500: Remove ab8500_regulator_debug_init/exit()

CONFIG_REGULATOR_AB8500_DEBUG is always not defined.
ab8500_regulator_debug_init() is not called at all now,
ab8500_regulator_debug_exit() simply return 0, thus remove them.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>