USB: usbip: missing lock in stub down

Missing lock in sysfs operation when we want to close the connection in order
to check the status and send the down event in a safe way.

Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20221003091016.641900-1-jtornosm@redhat.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>