[SERIAL] Remove incorrect code from ioc4 serial driver

Serial drivers in general should not write uart_info->flags - they're
private to serial_core.  Serial drivers have no need to fiddle with
tty->alt_speed, nor manipulate TTY_IO_ERROR in tty->flags.  Fix the
ioc4 serial driver for both these points by simply removing the
offending code.

Acked-by:  <pfg@sgi.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>