nvme: fix Write Zeroes limitations

commit b94e8cd2 upstream.

We voluntarily limit the Write Zeroes sizes to the MDTS value provided by
the hardware, but currently get the units wrong, so fix that.

Fixes: 6e02318e ("nvme: add support for the Write Zeroes command")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Tested-by: Klaus Jensen <k.jensen@samsung.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>