Documenation: Update location of docproc.c

docproc.c was moved in 2011 from scripts/basic to scripts
-> updated the references accordingly

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/kernel-doc-nano-HOWTO.txt

@@ -128,7 +128,7 @@ are:
   special place-holders for where the extracted documentation should
   go.
 
-- scripts/basic/docproc.c
+- scripts/docproc.c
 
   This is a program for converting SGML template files into SGML
   files. When a file is referenced it is searched for symbols