CVE-2019-6501: qemu stretch & jessie not-affected

The overflow was introduced in a71c775b24. Before that, page_len was
neither read from r->buf nor used as index to write the 0xb0 blocks
limit page.

FTR, this piece of code was later moved to the scsi_handle_inquiry_reply
helper in https://git.qemu.org/?p=qemu.git;a=commit;h=0a96ca2437.