clk: wm831x: Initialise wm831x pointer on init

commit 08442ce993deeb15a070c14cc3f3459e87d111e0 upstream.

Otherwise any attempt to interact with the hardware will crash. This is
what happens when drivers get written blind.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>