bonding: Invert test

Make the error case return early.
Make the normal return at the bottom of the function.
Reduces indent for readability.

Signed-off-by: Joe Perches <joe@perches.com>
Reviewed-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>