bridge: simplify br_getlink() a bit

Static checkers complain that we should maybe set "ret" before we do the
"goto out;".  They interpret the NULL return from br_port_get_rtnl() as
a failure and forgetting to set the error code is a common bug in this
situation.

The code is confusing but it's actually correct.  We are returning zero
deliberately.  Let's re-write it a bit to be more clear.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>