mfd: Fix pm8606 build failure

Reported by Andrew Morton <akpm@linux-foundation.org>, with
i386 allmodconfig:

ERROR: "pm8606_osc_disable" [drivers/video/backlight/88pm860x_bl.ko] undefined!
ERROR: "pm8606_osc_enable" [drivers/video/backlight/88pm860x_bl.ko] undefined!
ERROR: "pm8606_osc_disable" [drivers/leds/leds-88pm860x.ko] undefined!
ERROR: "pm8606_osc_enable" [drivers/leds/leds-88pm860x.ko] undefined!
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

drivers/mfd/88pm860x-core.c

@@ -542,6 +542,7 @@ int pm8606_osc_enable(struct pm860x_chip *chip, unsigned short client)
 	mutex_unlock(&chip->osc_lock);
 	return ret;
 }
+EXPORT_SYMBOL(pm8606_osc_enable);
 
 int pm8606_osc_disable(struct pm860x_chip *chip, unsigned short client)
 {
@@ -580,6 +581,7 @@ int pm8606_osc_disable(struct pm860x_chip *chip, unsigned short client)
 	mutex_unlock(&chip->osc_lock);
 	return ret;
 }
+EXPORT_SYMBOL(pm8606_osc_disable);
 
 static void __devinit device_osc_init(struct i2c_client *i2c)
 {