drm/amd/display: Remove return value of Calculate256BBlockSizes

The function Calculate256BBlockSizes always returns true, regardless of
the parameters. As any file checks the return of the function, this
commit changes the return value to void.

Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>