tty: sunsu: remove unused serial_icr_read()

It is commented and never used.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Link: https://lore.kernel.org/r/20250317070046.24386-25-jirislaby@kernel.org


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