bridge: cleanup: remove unneed check

We dereference "port" on the lines immediately before and immediately
after the test so port should hopefully never be null here.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>