nvme: PEL need to check gen number for verification of collected log

nvme: PEL need to check gen number for verification of collected log

If the Persistent Event Log is not read with a single Get Log Page
command, then host software should read the Generation Number field in
the Persistent Event Log header after establishing a reporting context
but before reading the remainder of the log and then re-read the
Generation Number field after it has read the entire log.

If the generation numbers do not match, then:
    - the reporting context may have been lost while reading the log;
    - the Persistent Event Log contents read may be invalid; and
    - host software should re-read the log.

While at it, fix bug (unallocated pointer free)

Signed-off-by: Steven Seungcheol Lee <sc108.lee@samsung.com>
[dwagner: ported from monolitic branch and updated context]
Signed-off-by: Daniel Wagner <dwagner@suse.de>