regulator: Include the device name in the microamps_requested_ file

We may have multiple devices requesting a supply with the same name so
include the device name in the generated filename for microamps_requested
to avoid duplicate files.

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