NET: mkiss: Fix typo

This typo was introduced by 5793f4be on
October 14, 2005 ...

Reported-by: Matti Aarnio <matti.aarnio@zmailer.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>