hwmon: (pmbus/mp2975) Add missed POUT attribute for page 1 mp2975 controller

hwmon: (pmbus/mp2975) Add missed POUT attribute for page 1 mp2975 controller

[ Upstream commit 2292e2f685cd5c65e3f47bbcf9f469513acc3195 ]

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

Fixes: 2c6fcbb21149 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>