staging: unisys: visorbus: add timeout to controlvm_periodic_work

Limit the amount that gets pulled from the queue on each try so we don't
get stuck in an infinite loop if something has gone wrong with the s-Par
firmware.

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