tty: serial: uartlite: register uart driver in init

tty: serial: uartlite: register uart driver in init

When two instances of uart devices are probing, a concurrency race can
occur. If one thread calls uart_register_driver function, which first
allocates and assigns memory to 'uart_state' member of uart_driver
structure, the other instance can bypass uart driver registration and
call ulite_assign. This calls uart_add_one_port, which expects the uart
driver to be fully initialized. This leads to a kernel panic due to a
null pointer dereference:

[    8.143581] BUG: kernel NULL pointer dereference, address: 00000000000002b8
[    8.156982] #PF: supervisor write access in kernel mode
[    8.156984] #PF: error_code(0x0002) - not-present page
[    8.156986] PGD 0 P4D 0
...
[    8.180668] RIP: 0010:mutex_lock+0x19/0x30
[    8.188624] Call Trace:
[    8.188629]  ? __die_body.cold+0x1a/0x1f
[    8.195260]  ? page_fault_oops+0x15c/0x290
[    8.209183]  ? __irq_resolve_mapping+0x47/0x80
[    8.209187]  ? exc_page_fault+0x64/0x140
[    8.209190]  ? asm_exc_page_fault+0x22/0x30
[    8.209196]  ? mutex_lock+0x19/0x30
[    8.223116]  uart_add_one_port+0x60/0x440
[    8.223122]  ? proc_tty_register_driver+0x43/0x50
[    8.223126]  ? tty_register_driver+0x1ca/0x1e0
[    8.246250]  ulite_probe+0x357/0x4b0 [uartlite]

To prevent it, move uart driver registration in to init function. This
will ensure that uart_driver is always registered when probe function
is called.

Signed-off-by: Jakub Lewalski <jakub.lewalski@nokia.com>
Signed-off-by: Elodie Decerle <elodie.decerle@nokia.com>
Link: https://lore.kernel.org/r/20250331160732.2042-1-elodie.decerle@nokia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>