serial: jsm: fix NPE during jsm_uart_port_init

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

serial: jsm: fix NPE during jsm_uart_port_init

No device was set which caused serial_base_ctrl_add to crash.

BUG: kernel NULL pointer dereference, address: 0000000000000050

Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI

CPU: 16 UID: 0 PID: 368 Comm: (udev-worker) Not tainted 6.12.25-amd64 #1 Debian 6.12.25-1

RIP: 0010:serial_base_ctrl_add+0x96/0x120

Call Trace:

<TASK>

serial_core_register_port+0x1a0/0x580

? __setup_irq+0x39c/0x660

? __kmalloc_cache_noprof+0x111/0x310

jsm_uart_port_init+0xe8/0x180 [jsm]

jsm_probe_one+0x1f4/0x410 [jsm]

local_pci_probe+0x42/0x90

pci_device_probe+0x22f/0x270

really_probe+0xdb/0x340

? pm_runtime_barrier+0x54/0x90

? __pfx___driver_attach+0x10/0x10

__driver_probe_device+0x78/0x110

driver_probe_device+0x1f/0xa0

__driver_attach+0xba/0x1c0

bus_for_each_dev+0x8c/0xe0

bus_add_driver+0x112/0x1f0

driver_register+0x72/0xd0

jsm_init_module+0x36/0xff0 [jsm]

? __pfx_jsm_init_module+0x10/0x10 [jsm]

do_one_initcall+0x58/0x310

do_init_module+0x60/0x230

Tested with Digi Neo PCIe 8 port card.