regulator/ab8500: move dereference below the check for NULL

I moved the dereference of "ab8500" below the check for NULL.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>