hwmon: (dell-smm) Update Documentation regarding firmware bugs

When adding the Inspiron 3505 to the fan type blacklist,
the Documentation was not updated to mention the firmware
bug on this machine.
Fix that.

Fixes: 6ba463ed (hwmon: (dell-smm) Add Inspiron 3505 to fan type blacklist)
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20220424154824.9396-1-W_Armin@gmx.deSigned-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/dell-smm-hwmon.rst

@@ -331,6 +331,8 @@ Reading of fan types causes erratic fan behaviour.      Studio XPS 8000
 
                                                         Inspiron 580
 
+                                                        Inspiron 3505
+
 Fan-related SMM calls take too long (about 500ms).      Inspiron 7720
 
                                                         Vostro 3360