Staging: comedi: amplc_dio200: Protect counter subdevice with spinlock

The internal state of an 82C54 counter timer chip will get messed up if
several threads read, write, configure, or check the status of the chip
simultaneously.  Protect the register access sequences with a spin lock.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>