staging: unisys: visornic: don't destroy global workqueues until devs destroyed

visornic_cleanup() was previously incorrectly destroying its global
workqueues prior to cleaning up the devices which used them.  This patch
corrects the order of these operations.

Signed-off-by: Tim Sell <Timothy.Sell@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>