tty: serial: altera_uart_{r,t}x_chars() need only uart_port

tty: serial: altera_uart_{r,t}x_chars() need only uart_port

Both altera_uart_{r,t}x_chars() need only uart_port, not altera_uart. So
pass the former from altera_uart_interrupt() directly.

Apart it maybe saves a dereference, this makes the transition of
altera_uart_tx_chars() easier to follow in the next patch.

Cc: Tobias Klauser <tklauser@distanz.ch>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Acked-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220920052049.20507-4-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>