scripts/spelling.txt: add more spellings to spelling.txt

Here are some of the more common spelling mistakes and typos that I've
found while fixing up spelling mistakes in the kernel over the past few
months.  Developers keep on coming up with more inventive ways to spell
words.

Link: http://lkml.kernel.org/r/20190618134807.9729-1-colin.king@canonical.com
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>