make INIT_FS use the __RW_LOCK_UNLOCKED initialization

[AV: rediffed on top of unification of init_fs]
Initialization of init_fs still uses the deprecated RW_LOCK_UNLOCKED macro.
This patch updates it to use the __RW_LOCK_UNLOCKED(lock) macro.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -2897,6 +2897,6 @@ EXPORT_SYMBOL(generic_readlink);
 /* to be mentioned only in INIT_TASK */
 struct fs_struct init_fs = {
 	.count		= ATOMIC_INIT(1),
-	.lock		= RW_LOCK_UNLOCKED,
+	.lock		= __RW_LOCK_UNLOCKED(init_fs.lock),
 	.umask		= 0022,
 };