serial: pass state to __uart_start() directly

__uart_start() does not need a tty struct. It works only with
uart_state. So pass the latter directly.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20230712081811.29004-8-jirislaby@kernel.org


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