hw/block/nvme: fix ns attachment out-of-bounds read

hw/block/nvme: fix ns attachment out-of-bounds read

nvme_ns_attachment() does not verify the contents of the host-supplied
16 bit "Number of Identifiers" field in the command payload.

Make sure the value is capped at 2047 and fix the out-of-bounds read.

Fixes: 645ce1a70cb6 ("hw/block/nvme: support namespace attachment command")
Cc: Minwoo Im <minwoo.im.dev@gmail.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
Reviewed-by: Minwoo Im <minwoo.im.dev@gmail.com>