cve-check: fix comments

This implements various fixes in comments in cve-check.bbclass
In particular, the "whitlisted" typo is important as the "whitelisted"
word is going to be replaced in a near future.

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>