regulator: Fix support for deviceless supply mappings

The patch to add support for looking up consumers by device name
had the side effect of causing us to require a device which is
at best premature since at least cpufreq still operates outside
the device model. Remove that requirement.

Reported-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>