docproc: Move printk file location

> docproc: kernel/printk.c: No such file or directory

So rename the file.
Signed-off-by: Joe Perches <joe@perches.com>
Noticed-by: kbuild test robot <fengguang.wu@intel.com>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/DocBook/device-drivers.tmpl

@@ -84,7 +84,7 @@ X!Iinclude/linux/kobject.h
 
      <sect1><title>Kernel utility functions</title>
 !Iinclude/linux/kernel.h
-!Ekernel/printk.c
+!Ekernel/printk/printk.c
 !Ekernel/panic.c
 !Ekernel/sys.c
 !Ekernel/rcupdate.c