In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Link: http://lkml.kernel.org/r/20171020191058.GA24427@embeddedor.comSigned-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>