RAID6_USE_EMPTY_ZERO_PAGE is unused and hardcoded to 0, so let's drop it.
Signed-off-by: NGiulio Benetti <giulio.benetti@benettiengineering.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NSong Liu <song@kernel.org>