VFS: Unexport do_kern_mount() and clean up simple_pin_fs()

Replace all module uses with the new vfs_kern_mount() interface, and fix up
simple_pin_fs().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/super.c b/fs/super.c
index 848be4f..15f2afd 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -864,11 +864,9 @@
 	return mnt;
 }
 
-EXPORT_SYMBOL_GPL(do_kern_mount);
-
 struct vfsmount *kern_mount(struct file_system_type *type)
 {
-	return do_kern_mount(type->name, 0, type->name, NULL);
+	return vfs_kern_mount(type, 0, type->name, NULL);
 }
 
 EXPORT_SYMBOL(kern_mount);