Fix up a couple of field names in the CREDITS file

Fix up a couple of field names in the CREDITS file

Ozgur Karatas reported that the very first entry in the CREDITS file had
the wrong tag for name (M: instead of N: - it happened when moving the
entry from the MAINTAINERS file, where 'M:' stands for "Maintainer").

And when I went looking, I found a couple of other cases of wrong
tagging too.

Reported-by: Ozgur Karatas <mueddib@yandex.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>