regulator: Initialise wm831x structure pointor for ISINK driver

The version that made it into mainline missed the initialisation of the
chip handle.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>
diff --git a/drivers/regulator/wm831x-isink.c b/drivers/regulator/wm831x-isink.c
index 1d8d987..4885700 100644
--- a/drivers/regulator/wm831x-isink.c
+++ b/drivers/regulator/wm831x-isink.c
@@ -167,6 +167,8 @@
 		return -ENOMEM;
 	}
 
+	isink->wm831x = wm831x;
+
 	res = platform_get_resource(pdev, IORESOURCE_IO, 0);
 	if (res == NULL) {
 		dev_err(&pdev->dev, "No I/O resource\n");