[CONNECTOR]: Return proper error code in cn_call_callback()

Error code should be set to EINVAL instead of ENODEV if !queue_work().
There's another call of queue_work() which may set err to EINVAL.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>