NET: NETROM: Cleanup argument SIOCADDRT ioctl argument checking.

nr_route.ndigis is unsigned int so the nr_route.ndigis < 0 expression is
never true and can be dropped.  Doing the nr_ax25_dev_get call later
allows the nr_route.ndigis test to bail out without having to dev_put.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Thomas Osterried <thomas@osterried.de>
Signed-off-by: David S. Miller <davem@davemloft.net>