scripts/gdb: rename pool_index to pool_index_plus_1

scripts/gdb: rename pool_index to pool_index_plus_1

We encounter the following issue after commit a6c1d9cb9a68 ("stackdepot:
rename pool_index to pool_index_plus_1").

(gdb) lx-dump-page-owner --pfn 262144
...
Python Exception <class 'gdb.error'>: There is no member named pool_index.
Error occurred in Python: There is no member named pool_index.

We rename pool_index to pool_index_plus_1 to fix this issue.

Link: https://lkml.kernel.org/r/20240619074911.100434-7-kuan-ying.lee@canonical.com
Fixes: a6c1d9cb9a68 ("stackdepot: rename pool_index to pool_index_plus_1")
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: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>