mfd: rk808: Make PM function declaration static

Avoids:
  ../drivers/mfd/rk808.c:771:1: warning: symbol 'rk8xx_pm_ops' \
    was not declared. Should it be static?

Fixes: 5752bc43 ("mfd: rk808: Mark pm functions __maybe_unused")
Reviewed-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

drivers/mfd/rk808.c

@@ -768,7 +768,7 @@ static int __maybe_unused rk8xx_resume(struct device *dev)
 
 	return ret;
 }
-SIMPLE_DEV_PM_OPS(rk8xx_pm_ops, rk8xx_suspend, rk8xx_resume);
+static SIMPLE_DEV_PM_OPS(rk8xx_pm_ops, rk8xx_suspend, rk8xx_resume);
 
 static struct i2c_driver rk808_i2c_driver = {
 	.driver = {