staging: comedi: usbduxfast: remove unnecessary semaphore down/up

The semaphore down/up in usbduxfast_attach_common() is not necessary.
This function is only called as part of the (*auto_attach) and does
not talk to the USB device.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>