regulator: pfuze100-regulator: Remove global variable

We should better not use a global 'struct pfuze_regulator' variable,
as this could cause problems if multiple regulator chips are used.

Place it inside the private struct instead.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>