hw/nvme: fix oob memory read in fdp events log

hw/nvme: fix oob memory read in fdp events log

As reported by Trend Micro's Zero Day Initiative, an oob memory read
vulnerability exists in nvme_fdp_events(). The host-provided offset is
not verified.

Fix this.

This is only exploitable when Flexible Data Placement mode (fdp=on) is
enabled.

Fixes: CVE-2023-4135
Fixes: 73064edfb864 ("hw/nvme: flexible data placement emulation")
Reported-by: Trend Micro's Zero Day Initiative
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
(cherry picked from commit ecb1b7b082d3b7dceff0e486a114502fc52c0fdf)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>