cris: fix a build error in drivers/tty/serial/crisv10.c

Fix these errors:

    drivers/tty/serial/crisv10.c:4453: error: 'if_ser0' undeclared (first use in this function): 2 errors in 2 logs
    drivers/tty/serial/crisv10.c:4453: error: (Each undeclared identifier is reported only once: 2 errors in 2 logs
    drivers/tty/serial/crisv10.c:4453: error: for each function it appears in.): 2 errors in 2 logs

"if_ser0" is a typo, it should be "if_serial_0".

Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Mikael Starvik <starvik@axis.com>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>