i2c: rcar: disable runtime PM correctly in slave mode

When we also are I2C slave, we need to disable runtime PM because the
address detection mechanism needs to be active all the time. However, we
can reenable runtime PM once the slave instance was unregistered. So,
use pm_runtime_get_sync/put to achieve this, since it has proper
refcounting. pm_runtime_allow/forbid is like a global knob controllable
from userspace which is unsuitable here.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org

drivers/i2c/busses/i2c-rcar.c

@@ -576,7 +576,7 @@ static int rcar_reg_slave(struct i2c_client *slave)
 	if (slave->flags & I2C_CLIENT_TEN)
 		return -EAFNOSUPPORT;
 
-	pm_runtime_forbid(rcar_i2c_priv_to_dev(priv));
+	pm_runtime_get_sync(rcar_i2c_priv_to_dev(priv));
 
 	priv->slave = slave;
 	rcar_i2c_write(priv, ICSAR, slave->addr);
@@ -598,7 +598,7 @@ static int rcar_unreg_slave(struct i2c_client *slave)
 
 	priv->slave = NULL;
 
-	pm_runtime_allow(rcar_i2c_priv_to_dev(priv));
+	pm_runtime_put(rcar_i2c_priv_to_dev(priv));
 
 	return 0;
 }