mfd: Add placeholders for WM8350 client devices

In order to avoid merge problems further down the line add placeholders
for several of the WM8350 client devices and register them, otherwise
the patches adding the client devices will all try to update the same
code.

Also remove redundant checks for null regulator platform devices while
we're at it.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Samuel Ortiz <sameo@openedhand.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>