Now that the driver has been converted to use one regmap per port, change
efr locking to operate on a channel basis instead of on the whole IC.

Fixes: 3837a037 ("serial: sc16is7xx: improve regmap debugfs by using one regmap per port")
Cc:  <stable@vger.kernel.org> # 6.1.x: 3837a037 serial: sc16is7xx: improve regmap debugfs by using one regmap per port
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20231211171353.2901416-5-hugo@hugovil.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>