regulator: 88pm800: Update driver to use devm_regulator_register fn

regulator: 88pm800: Update driver to use devm_regulator_register fn

This patch replaces standard regulator_register with
devm_regulator_register() fn, as using devm_regulator_register() fn
simplifies the driver return/exit path.

As part of this update, patch also cleanups up all unnecessary changes
which is result of this patch -

  - Remove _remove() fn, as devm_ variant takes care of it.
  - Remove pm800_regulators.regulators[] field, as it was only
    needed during cleanup, so we no longer need this.
    This also saved some amount of memory.

Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>