tty: make tty_port_client_operations operate with u8

The parameters are already unsigned chars. So make them explicitly u8s,
as the rest is going to be unified to u8 eventually too.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230810091510.13006-10-jirislaby@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>