fs/9p: remove sparse warning in vfs_inode

make v9fs_dentry_from_dir_inode static

Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 75c261f..6e94f32 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -260,7 +260,7 @@
  *
  */
 
-struct dentry *v9fs_dentry_from_dir_inode(struct inode *inode)
+static struct dentry *v9fs_dentry_from_dir_inode(struct inode *inode)
 {
 	struct dentry *dentry;