ethtool: ethnl_set_linkmodes: remove redundant null check

info cannot be NULL here since its being accessed earlier
in the function: nlmsg_parse(info->nlhdr...). Remove this
redundant NULL check.

Signed-off-by: Gaurav Singh <gaurav1086@gmail.com>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>