Per datasheet, the chip ID for LTM4676 is 0x448x. This was observed
in real systems. In addition to that, chip ID 0x4401 was observed
as well. Research shows that the chip ID has been changed from 0x440x
to 0x448x in datasheet revision C. Add support for the additional chip ID.

Also add the chip ID for LTM4676A, which is functionally identical
to LTM4676.
Reported-by: Ananda Babu Nettam <anandab@juniper.net>
Cc: Ananda Babu Nettam <anandab@juniper.net>
Cc: Amit U Jain <amjain@juniper.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>