bridge: fix error handling in br_add_if()

When device is added to bridge its refcnt is incremented (in new_nbp()), but if
error occurs during further br_add_if() operations this counter is not
decremented back. Fix it by adding dev_put() call in the error path.

Signed-off-by: Volodymyr G Lukiianyk <volodymyrgl@gmail.com>
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>