mfd: wm5110: Set FX_CTRL2 to volatile

FX_CTRL2 is a volatile register and should be marked as such, this patch
does so.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/wm5110-tables.c b/drivers/mfd/wm5110-tables.c
index 4903265..3113e39 100644
--- a/drivers/mfd/wm5110-tables.c
+++ b/drivers/mfd/wm5110-tables.c
@@ -2349,6 +2349,7 @@
 	case ARIZONA_IRQ_PIN_STATUS:
 	case ARIZONA_AOD_IRQ1:
 	case ARIZONA_AOD_IRQ2:
+	case ARIZONA_FX_CTRL2:
 	case ARIZONA_ASRC_STATUS:
 	case ARIZONA_DSP_STATUS:
 	case ARIZONA_DSP1_CONTROL_1: