Avoid possible NULL pointer deref in 3c359 driver

In xl_freemem(), if dev_if is NULL, the line

  struct xl_private *xl_priv =(struct xl_private *)dev->priv;

will cause a NULL pointer dereference.

(akpm: don't try to fix it: just delete the pointless test-for-null)

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>