x86: geode: fix hwrng register accesses

x86: geode: fix hwrng register accesses

When the membase and pci_dev pointer were moved to a new struct in priv,
the actual membase users were left untouched, and they started reading
out arbitrary memory behind the struct instead of registers. This
unfortunately turned the RNG into a constant number generator, depending
on the content of what was at that offset.

To fix this, update geode_rng_data_{read,present}() to also get the
membase via amd_geode_priv, and properly read from the right addresses
again.

Closes #13417.

Reported-by: Timur I. Davletshin <[email protected]>
Tested-by: Timur I. Davletshin <[email protected]>
Suggested-by: Jo-Philipp Wich <[email protected]>
Signed-off-by: Jonas Gorski <[email protected]>