mISDN: hfcpci: Fix warning when deleting uninitialized timer

In the Linux kernel, the following vulnerability has been resolved:

mISDN: hfcpci: Fix warning when deleting uninitialized timer

With CONFIG_DEBUG_OBJECTS_TIMERS unloading hfcpci module leads
to the following splat:

[ 250.215892] ODEBUG: assert_init not available (active state 0) object: ffffffffc01a3dc0 object type: timer_list hint: 0x0
[ 250.217520] WARNING: CPU: 0 PID: 233 at lib/debugobjects.c:612 debug_print_object+0x1b6/0x2c0
[ 250.218775] Modules linked in: hfcpci(-) mISDN_core
[ 250.219537] CPU: 0 UID: 0 PID: 233 Comm: rmmod Not tainted 6.17.0-rc2-g6f713187ac98 #2 PREEMPT(voluntary)
[ 250.220940] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 250.222377] RIP: 0010:debug_print_object+0x1b6/0x2c0
[ 250.223131] Code: fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 75 4f 41 56 48 8b 14 dd a0 4e 01 9f 48 89 ee 48 c7 c7 20 46 01 9f e8 cb 84d
[ 250.225805] RSP: 0018:ffff888015ea7c08 EFLAGS: 00010286
[ 250.226608] RAX: 0000000000000000 RBX: 0000000000000005 RCX: ffffffff9be93a95
[ 250.227708] RDX: 1ffff1100d945138 RSI: 0000000000000008 RDI: ffff88806ca289c0
[ 250.228993] RBP: ffffffff9f014a00 R08: 0000000000000001 R09: ffffed1002bd4f39
[ 250.230043] R10: ffff888015ea79cf R11: 0000000000000001 R12: 0000000000000001
[ 250.231185] R13: ffffffff9eea0520 R14: 0000000000000000 R15: ffff888015ea7cc8
[ 250.232454] FS: 00007f3208f01540(0000) GS:ffff8880caf5a000(0000) knlGS:0000000000000000
[ 250.233851] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 250.234856] CR2: 00007f32090a7421 CR3: 0000000004d63000 CR4: 00000000000006f0
[ 250.236117] Call Trace:
[ 250.236599] <TASK>
[ 250.236967] ? trace_irq_enable.constprop.0+0xd4/0x130
[ 250.237920] debug_object_assert_init+0x1f6/0x310
[ 250.238762] ? __pfx_debug_object_assert_init+0x10/0x10
[ 250.239658] ? __lock_acquire+0xdea/0x1c70
[ 250.240369] __try_to_del_timer_sync+0x69/0x140
[ 250.241172] ? __pfx___try_to_del_timer_sync+0x10/0x10
[ 250.242058] ? __timer_delete_sync+0xc6/0x120
[ 250.242842] ? lock_acquire+0x30/0x80
[ 250.243474] ? __timer_delete_sync+0xc6/0x120
[ 250.244262] __timer_delete_sync+0x98/0x120
[ 250.245015] HFC_cleanup+0x10/0x20 [hfcpci]
[ 250.245704] __do_sys_delete_module+0x348/0x510
[ 250.246461] ? __pfx___do_sys_delete_module+0x10/0x10
[ 250.247338] do_syscall_64+0xc1/0x360
[ 250.247924] entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fix this by initializing hfc_tl timer with DEFINE_TIMER macro.
Also, use mod_timer instead of manual timeout update.