ipv4: remove redundant assignment to n

The pointer n is being assigned a value however this value is
never read in the code block and the end of the code block
continues to the next loop iteration. Clean up the code by
removing the redundant assignment.

Fixes: 1bff1a0c

 ("ipv4: Add function to send route updates")
Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>