hw/nvme: Change alignment in dma functions for nvme_blk_*

hw/nvme: Change alignment in dma functions for nvme_blk_*

Since the nvme_blk_read/write are used by both the data and metadata
portions of the IO, it can't have the 512B alignment requirement.
Without this change any metadata transfer, which length isn't a multiple
of 512B and which is bigger than 512B, will result in only a partial
transfer.

Signed-off-by: Mateusz Kozlowski <kozlowski.mateuszpl@gmail.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>