kernel-doc: restrict syntax for private: and public:

scripts/kernel-doc can (incorrectly) delete struct members that are
surrounded by /* ...  */ <struct members> /* ...  */ if there is a /*
private: */ comment in there somewhere also.

Fix that by making the "/* private:" only allow whitespace between /* and
"private:", not anything/everything in the world.

This fixes some erroneous kernel-doc warnings that popped up while
processing include/linux/usb/composite.h.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/kernel-doc-nano-HOWTO.txt

@@ -269,7 +269,10 @@ Use the argument mechanism to document members or constants.
 
 Inside a struct description, you can use the "private:" and "public:"
 comment tags.  Structure fields that are inside a "private:" area
-are not listed in the generated output documentation.
+are not listed in the generated output documentation.  The "private:"
+and "public:" tags must begin immediately following a "/*" comment
+marker.  They may optionally include comments between the ":" and the
+ending "*/" marker.
 
 Example:
 
@@ -283,7 +286,7 @@ Example:
 struct my_struct {
     int a;
     int b;
-/* private: */
+/* private: internal use only */
     int c;
 };