serial: ioc4_serial: Staticize ioc4_serial_attach_one()

ioc4_serial_attach_one() is used only in this file.
Also, ioc4_serial is not used; it can be removed.
Fix the following sparse warnings:

drivers/tty/serial/ioc4_serial.c:300:3: warning: symbol 'ioc4_serial' was not declared. Should it be static?
drivers/tty/serial/ioc4_serial.c:2771:1: warning: symbol 'ioc4_serial_attach_one' was not declared. Should it be static?

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Patrick Gefre <pfg@sgi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>