scripts/gdb: fix lx-timerlist for struct timequeue_head change

scripts/gdb: fix lx-timerlist for struct timequeue_head change

commit 511885d7061e ("lib/timerqueue: Rely on rbtree semantics for next
timer") changed struct timerqueue_head, and so print_active_timers()
should be changed accordingly with its way to interpret the structure.

Link: https://lkml.kernel.org/r/TYCP286MB21463BD277330B26DDC18903C6819@TYCP286MB2146.JPNP286.PROD.OUTLOOK.COM
Signed-off-by: Peng Liu <liupeng17@lenovo.com>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>