mfd: ab8500: ensure new AB8500 pinctrl driver is probed correctly

The old, BROKEN AB8500 GPIO driver has been revamped as a shiny
new pinctrl driver and has been renamed as such. So, if we would
like to make use of it, we need to register it via its new name.

Cc: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>