drivers: regulator: core: convert to using pr_ macros

The regulator framework uses a lot of printks with a
specific formatting using __func__. This converts them
to use pr_ calls with a central format string.

Cc: bleong@codeaurora.org
Signed-off-by: Daniel Walker <dwalker@codeaurora.org>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>