regulator: Clean up logging a bit

The recent introduction of standard regulator API logging macros means
that all our log messages have at least the function name in them and
logging that the constraints are for the regulator API is probably a
bit much.

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