regulator: mp886x: use .probe_new

Use the new .probe_new for mp886x. It does not use the const
struct i2c_device_id * argument, so convert it to utilise the
simplified i2c driver registration.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Link: https://lore.kernel.org/r/20200702100200.1a4c65d1@xhacker.debian
Signed-off-by: Mark Brown <broonie@kernel.org>