mfd: Ensure value written by wm831x_set_bits() is within the mask

Purely for defensiveness.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/wm831x-core.c

diff --git a/drivers/mfd/wm831x-core.c b/drivers/mfd/wm831x-core.c
index 772fe58..baae9e4 100644
--- a/drivers/mfd/wm831x-core.c
+++ b/drivers/mfd/wm831x-core.c
@@ -295,7 +295,7 @@
 		goto out;
 
 	r &= ~mask;
-	r |= val;
+	r |= val & mask;
 
 	ret = wm831x_write(wm831x, reg, 2, &r);