drivers/net/tokenring/olympic.c: fix warning

When dev_name() is changed to return `const char *':

drivers/net/tokenring/olympic.c: In function 'olympic_probe':
drivers/net/tokenring/olympic.c:234: warning: assignment discards qualifiers from pointer target type

Cc: Jeff Garzik <jeff@garzik.org>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>