staging: unisys: visornic: prevent double-unlock of priv_lock

Previously, devdata->priv_lock was being unlocked in visornic_serverdown()
both before calling visornic_serverdown_complete(), then again at the end
of the function.  This bug was corrected.

The structure of visornic_serverdown() was also improved to make it easier
to follow and to decrease the chance that such bugs will be introduced
again.  The main-path logic now falls thru down the left-side of the page,
with a common error-exit point to handle error conditions.

Signed-off-by: Tim Sell <Timothy.Sell@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>