checkpatch.pl: modify warning message for printk usage
Modify warning message when printk is used in a patch. It mentions to
use subsystem_dbg instead of netdev_dbg as the first preferred format of
logging debug messages.
Signed-off-by: Yogesh Chaudhari <mr.yogesh@gmail.com> Cc: Joe Perches <joe@perches.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>