[SERIAL] ip22zilog: Fix oops on runlevel change with serial console

Incorrect uart_write_wakeup() calls cause reference to a NULL tty
pointer.  This has been fixed in the sunsab and sunzilog serial drivers
in October 2005.  Update the ip22zilog, which is based on sunzilog,
accordingly.

Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>