hwmon: (adt7410) Document ADT7420 support

The adt7410 driver supports the ADT7420, but its documentation file
makes no mention of that. Add this refrence, and a brief a description
of the differences between the ADT7410 and the ADT7420.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Hartmut Knaack <knaack.h@gmx.de>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/adt7410

@@ -4,9 +4,14 @@ Kernel driver adt7410
 Supported chips:
   * Analog Devices ADT7410
     Prefix: 'adt7410'
-    Addresses scanned: I2C 0x48 - 0x4B
+    Addresses scanned: None
     Datasheet: Publicly available at the Analog Devices website
                http://www.analog.com/static/imported-files/data_sheets/ADT7410.pdf
+  * Analog Devices ADT7420
+    Prefix: 'adt7420'
+    Addresses scanned: None
+    Datasheet: Publicly available at the Analog Devices website
+               http://www.analog.com/static/imported-files/data_sheets/ADT7420.pdf
 
 Author: Hartmut Knaack <knaack.h@gmx.de>
 
@@ -27,6 +32,10 @@ value per second or even justget one sample on demand for power saving.
 Besides, it can completely power down its ADC, if power management is
 required.
 
+The ADT7420 is register compatible, the only differences being the package,
+a slightly narrower operating temperature range (-40°C to +150°C), and a
+better accuracy (0.25°C instead of 0.50°C.)
+
 Configuration Notes
 -------------------