staging: comedi: dyna_pci10xx: remove the 'start_stop_sem' mutex

The comedi core already has a mutex protecting the attach/detach
of the comedi drivers.

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