checkpatch: suggest pr_<level> over printk(KERN_<LEVEL>

Suggest the shorter pr_<level> instead of printk(KERN_<LEVEL>.

Prefer to use pr_<level> over bare printks.
Prefer to use pr_warn over pr_warning.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>