tty: rp2: remove unused rp2_uart_port::ignore_rx

tty: rp2: remove unused rp2_uart_port::ignore_rx

clang-struct [1] found rp2_uart_port::ignore_rx unused.

It was actually never used. Not even in introductory commit 7d9f49afa451
("serial: rp2: New driver for Comtrol RocketPort 2 cards").

[1] https://github.com/jirislaby/clang-struct

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: Kevin Cernekee <cernekee@gmail.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20231121103626.17772-6-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>