checkpatch: warn on logging continuations

pr_cont(...) and printk(KERN_CONT ...) uses should be discouraged
as their output can be interleaved by multiple logging processes.

Link: http://lkml.kernel.org/r/7100ba00098694ec81471a299583ed068975fd05.1483465888.git.joe@perches.com


Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>