Documentation: update header filename in CodingStyle

pr_info() and pr_debug() are in linux/printk.h, not linux/kernel.h.
Last updated is unnecessary, we have git for that.

Signed-off-by: Roland Kammerer <dev.rck@gmail.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Harry Wei <harryxiyou@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>