Add missed attribute for reading POUT from page 1.
It is supported by device, but has been missed in initial commit.

Fixes: 2c6fcbb2 ("hwmon: (pmbus) Add support for MPS Multi-phase mp2975 controller")
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20210927070740.2149290-1-vadimp@nvidia.com


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