test/py: remove hacks for non-zero RAM base address in tests

Some functions have different behaviour when the given address is 0
(assumed to be NULL by the function).

find_ram_base() does not return 0 anymore so it's safe to remove those
offsets.

Suggested-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>