hwmon: (nct6775) Fix fan6 detection for NCT6793D

Commit 2d99925a ("hwmon: (nct6775) Separate fan/pwm configuration
detection for NCT6793D") accidentally removed part of the code detecting
if fan6 is enabled or not. As result, fan6 is no longer detected on Asus
PRIME Z370-A. Restore the missing detection code.

Fixes: 2d99925a ("hwmon: (nct6775) Separate fan/pwm configuration detection for NCT6793D")
Reported-by: Chris Siebenmann <cks@cs.toronto.edu>
Cc: Chris Siebenmann <cks@cs.toronto.edu>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/nct6775.c

@@ -3594,7 +3594,8 @@ nct6775_check_fan_inputs(struct nct6775_data *data)
 			fan5pin |= cr1b & BIT(5);
 			fan5pin |= creb & BIT(5);
 
-			fan6pin = creb & BIT(3);
+			fan6pin = !dsw_en && (cr2d & BIT(1));
+			fan6pin |= creb & BIT(3);
 
 			pwm5pin |= cr2d & BIT(7);
 			pwm5pin |= (creb & BIT(4)) && !(cr2a & BIT(0));