hwmon: (pmbus/max31785) Support revision "B"

There was an issue in how the tach feedbacks of dual rotor fans were
reported during any change in fan speeds with revision "A" of the
MAX31785. When the fan speeds would transition to a new target speed,
the rotor not wired to the TACH input when TACHSEL = 0 would report a
speed of 0 until the new target was reached. This has been fixed,
resulting in a revision "B" update where the MFR_REVISION of "B" is
0x3061.

Signed-off-by: Matthew Barth <msbarth@linux.ibm.com>
Link: https://lore.kernel.org/r/20210201212217.73721-1-msbarth@linux.ibm.com
[groeck: Change 'ret' variable type to int]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>