net:dev: remove double indentical assignment in dev_change_net_namespace().

This patch removes double assignment of err to -EINVAL in dev_change_net_namespace().

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>