scripts/spelling.txt: add several more common spelling mistakes

Lately I've been cleaning up spelling mistakes in kernel error messages
and here are some of the more common spelling mistakes that I've found
which probably should be added to this list so we don't keep on seeing
them appearing again.

Link: http://lkml.kernel.org/r/20161209173326.17662-1-colin.king@canonical.com
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>