serial: max3100: Update uart_driver_registered on driver removal

stable inclusion
from stable-v4.19.316
commit 21a61a7fbcfdd3493cede43ebc7c4dfae2147a8b
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IA7D2Z
CVE: CVE-2024-38633

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21a61a7fbcfdd3493cede43ebc7c4dfae2147a8b



--------------------------------

[ Upstream commit 712a1fcb38dc7cac6da63ee79a88708fbf9c45ec ]

The removal of the last MAX3100 device triggers the removal of
the driver. However, code doesn't update the respective global
variable and after insmod — rmmod — insmod cycle the kernel
oopses:

  max3100 spi-PRP0001:01: max3100_probe: adding port 0
  BUG: kernel NULL pointer dereference, address: 0000000000000408
  ...
  RIP: 0010:serial_core_register_port+0xa0/0x840
  ...
   max3100_probe+0x1b6/0x280 [max3100]
   spi_probe+0x8d/0xb0

Update the actual state so next time UART driver will be registered
again.

Hugo also noticed, that the error path in the probe also affected
by having the variable set, and not cleared. Instead of clearing it
move the assignment after the successfull uart_register_driver() call.

Fixes: 7831d56b ("tty: MAX3100")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20240402195306.269276-3-andriy.shevchenko@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yi Yang <yiyang13@huawei.com>