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 4
months.

Link: http://lkml.kernel.org/r/20190114110215.1986-1-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>