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>

scripts/checkpatch.pl

@@ -2833,7 +2833,7 @@ sub process {
 			my $level2 = $level;
 			$level2 = "dbg" if ($level eq "debug");
 			WARN("PREFER_PR_LEVEL",
-			     "Prefer netdev_$level2(netdev, ... then dev_$level2(dev, ... then pr_$level(...  to printk(KERN_$orig ...\n" . $herecurr);
+			     "Prefer [subsystem eg: netdev]_$level2([subsystem]dev, ... then dev_$level2(dev, ... then pr_$level(...  to printk(KERN_$orig ...\n" . $herecurr);
 		}
 
 		if ($line =~ /\bpr_warning\s*\(/) {