fs: name case update method

smpfs and ncpfs want to update a live dentry name in-place. Rather than
have them open code the locking, provide a documented dcache API.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index cbfc956..6cdf499 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -290,6 +290,8 @@
 	return res;
 }
 
+extern void dentry_update_name_case(struct dentry *, struct qstr *);
+
 /* used for rename() and baskets */
 extern void d_move(struct dentry *, struct dentry *);
 extern struct dentry *d_ancestor(struct dentry *, struct dentry *);