scripts/gdb: fix lx-mounts command error

(gdb) lx-mounts
      mount          super_block     devname pathname fstype options
Python Exception <class 'gdb.error'>: There is no member named list.
Error occurred in Python: There is no member named list.

We encounter the above issue after commit 2eea9ce431 ("mounts: keep
list of mounts in an rbtree"). The commit move a mount from list into
rbtree.

So we can instead use rbtree to iterate all mounts information.

Link: https://lkml.kernel.org/r/20240723064902.124154-4-kuan-ying.lee@canonical.com
Fixes: 2eea9ce431 ("mounts: keep list of mounts in an rbtree")
Signed-off-by: Kuan-Ying Lee <kuan-ying.lee@canonical.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

scripts/gdb/linux/proc.py

@@ -18,6 +18,7 @@ from linux import utils
 from linux import tasks
 from linux import lists
 from linux import vfs
+from linux import rbtree
 from struct import *
 
 
@@ -172,8 +173,7 @@ values of that process namespace"""
         gdb.write("{:^18} {:^15} {:>9} {} {} options\n".format(
                   "mount", "super_block", "devname", "pathname", "fstype"))
 
-        for mnt in lists.list_for_each_entry(namespace['list'],
-                                             mount_ptr_type, "mnt_list"):
+        for mnt in rbtree.rb_inorder_for_each_entry(namespace['mounts'], mount_ptr_type, "mnt_node"):
             devname = mnt['mnt_devname'].string()
             devname = devname if devname else "none"