tty: serial: 8250: Fix port count mismatch with the device

Normally, the number of ports is indicated by the third digit of the
device ID on Moxa PCI serial boards. For example, `0x1121` indicates a
device with 2 ports.

However, `CP116E_A_A` and `CP116E_A_B` are exceptions; they have 8
ports, but the third digit of the device ID is `6`.

This patch introduces a function to retrieve the number of ports on Moxa
PCI serial boards, addressing the issue described above.

Fixes: 37058fd ("tty: serial: 8250: Add support for MOXA Mini PCIe boards")
Cc: stable <stable@kernel.org>
Signed-off-by: Crescent Hsieh <crescentcy.hsieh@moxa.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/20240617063058.18866-1-crescentcy.hsieh@moxa.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_pci.c

@@ -1985,6 +1985,17 @@ enum {
  MOXA_SUPP_RS485 = BIT(2),
 };
 
+static unsigned short moxa_get_nports(unsigned short device)
+{
+ switch (device) {
+ case PCI_DEVICE_ID_MOXA_CP116E_A_A:
+ case PCI_DEVICE_ID_MOXA_CP116E_A_B:
+ return 8;
+ }
+
+ return FIELD_GET(0x00F0, device);
+}
+
 static bool pci_moxa_is_mini_pcie(unsigned short device)
 {
  if (device == PCI_DEVICE_ID_MOXA_CP102N ||
@@ -2038,7 +2049,7 @@ static int pci_moxa_init(struct pci_dev *dev)
 {
  unsigned short device = dev->device;
  resource_size_t iobar_addr = pci_resource_start(dev, 2);
- unsigned int num_ports = (device & 0x00F0) >> 4, i;
+ unsigned int i, num_ports = moxa_get_nports(device);
  u8 val, init_mode = MOXA_RS232;
 
  if (!(pci_moxa_supported_rs(dev) & MOXA_SUPP_RS232)) {