linux/cve-exclusion: do not shift first_affected

linux/cve-exclusion: do not shift first_affected

Stop shifting first_affected if backport is indicated. This does not
have effect on generated list, but makes the logic cleaner as it will
not shift it to "first affected on our branch" and also make it behave
like in defaultStatus==affected case.

Cc: daniel.turull@ericsson.com
Signed-off-by: Peter Marko <peter.marko@siemens.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit dc1ecb69389dd79354084757ba6b9af0781afcc0)
Signed-off-by: Steve Sakoman <steve@sakoman.com>