serial: 8250_exar: Don't return positive values as error codes

PCI core may return positive codes for the specific errors.
There is a special API to convert them to negative stanrard ones.
Use that API to avoid returning positive values as error codes.

Fixes: f7ce070 ("serial: exar: add CTI specific setup code")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Parker Newman <pnewman@connecttech.com>
Link: https://lore.kernel.org/r/20240503171917.2921250-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: andy-shev

drivers/tty/serial/8250/8250_exar.c

@@ -1162,12 +1162,12 @@ static int cti_board_init_fpga(struct exar8250 *priv, struct pci_dev *pcidev)
 	// Enable external interrupts in special cfg space register
 	ret = pci_read_config_word(pcidev, CTI_FPGA_CFG_INT_EN_REG, &cfg_val);
 	if (ret)
-		return ret;
+		return pcibios_err_to_errno(ret);
 
 	cfg_val |= CTI_FPGA_CFG_INT_EN_EXT_BIT;
 	ret = pci_write_config_word(pcidev, CTI_FPGA_CFG_INT_EN_REG, cfg_val);
 	if (ret)
-		return ret;
+		return pcibios_err_to_errno(ret);
 
 	// RS485 gate needs to be enabled; otherwise RTS/CTS will not work
 	exar_write_reg(priv, CTI_FPGA_RS485_IO_REG, 0x01);