lantiq: fix etop compiler warnings

The following warnings are introduced by our own patches:

 lantiq_etop.c:173:1: warning: no semicolon at end of struct or union
 };
 ^
 lantiq_etop.c: In function 'ltq_etop_change_mtu':
 lantiq_etop.c:725:2: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
  int max = ETH_HLEN + VLAN_HLEN + new_mtu + ETH_FCS_LEN;
  ^~~

Signed-off-by: Mathias Kresin <dev@kresin.me>