hwmon: (pmbus/xdpe12284) Add callback for vout limits conversion

Provide read_word_data() callback for overvoltage and undervoltage
output readouts conversion. These registers are presented in
'slinear11' format, while default conversion for 'vout' class for the
devices is 'vid'. It is resulted in wrong conversion in pmbus_reg2data()
for in{3-4}_lcrit and in{3-4}_crit attributes.
)
Fixes: aaafb7c8 ("hwmon: (pmbus) Add support for Infineon Multi-phase xdpe122 family controllers")
Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Link: https://lore.kernel.org/r/20200224225202.19576-1-vadimp@mellanox.com


[gropeck: Adjusted to mainline PMBus API]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>