regulator: core: Prioritise consumer mappings over regulator name

Currently, when looking up a regulator supply, the regulator name
takes priority over the consumer mappings. As there are a lot of
regulator names that are in fairly common use (VDD, MICVDD, etc.) this
can easily lead to obtaining the wrong supply, when a system contains
two regulators that share a name.

The explicit consumer mappings contain much less ambiguity as they
specify both a name and a consumer device. As such prioritise those if
one exists and only fall back to the regulator name if there are no
matching explicit mappings.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>