regulator: tps6586x: Handle both enable reg/bits being the same

Change-Id: I40400bb65eab496bb1becd26b37a9653b99d4f41
Signed-off-by: Danny Huang <dahuang@nvidia.com>
Signed-off-by: Olof Johansson <olofj@chromium.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
  (Split into separate patches)
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>