hwmon: (lm90) Add partial PEC support for ADT7461

Revision 0 of the ADT7461 datasheet suggests that the chip supports PEC
(packet error checking). This information is gone in later versions of the
datasheet. Experiments show that PEC support on ADT7461 is similar to PEC
support in ADM1032, ie it is only supported for read operations. Add
support for it to the driver.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>