regulator: mc13783-regulator: correct the probing time.

When the mc13783-regulator driver is built in kernel, probing it during
the regulator subsystem initialisation result in a fault.

That is because regulator subsystem is planned to be initialised very early
in the boot process, before the mfd subsystem initialisation.

The mc12783-regulator probing process need to access to the mc13783-core
functionality to read/write mc13783 registers and so must be called after
the mc13783-core driver initialisation.

The way to do this is to let the kernel probe the mc13783-regulator driver when
mc13783-core register his regulator subdevice.

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