mfd: arizona: Add stub for wm5102_patch()

For the WM5102 there is a dependency in the core code on wm5102_patch()
which only exists when CONFIG_MFD_WM5102 is defined. To avoid having
to sprinkle #ifdefs around the code it is given an alternative empty
stub version when CONFIG_MFD_WM5102 is deselected

Signed-off-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>