checkpatch: remove %p4cn

%p4cn was recently removed and replaced by %p4chR in vsprintf. So,
remove the check for %p4cn from checkpatch.pl.

Fixes: 37eed892 ("vsprintf: Use %p4chR instead of %p4cn for reading data in reversed host ordering")
Signed-off-by: Aditya Garg <gargaditya08@live.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/PN3PR01MB959760B89BF7E4B43852700CB8832@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM


Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>