checkpatch: handle do without braces if we have enough context

If we have sufficient context detect and handle do without braces ({).
Else these incorrectly trigger a trailing statements error for the
associated while.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>