usbip: tools: fix fd leakage in the function of read_attr_usbip_status

We should close the fd before the return of read_attr_usbip_status.

Fixes: 3391ba0e

 ("usbip: tools: Extract generic code to be shared with vudc backend")
Signed-off-by: Hewenliang <hewenliang4@huawei.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20191025043515.20053-1-hewenliang4@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>