staging: comedi: amplc_dio200_common: remove 'spinlock' from struct dio200_subdev_8254

Currently this driver uses a spinlock in the 8254 subdevice (*insn_read), (*insn_write),
and (*insn_config) functions. The comedi core checks if the subdevice is 'busy', in
parse_insn(), before any of the subdevice functions are attempted.

Remove the unnecessary spinlock.

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>