changes to optimize scratchpad layout hurt performance on some arch

[0xsebb]

the scratchpad layout optimization hurts Performance at least on polaris 12 chip. It boils down to cache size, i guess. My hasrate sinks from 430h/s to 415h/s with the same settings. Changing the Settings does not help, these are optimal in both cases. A polaris 11 is not affected, but it does not benefit from the changes either.

[fireice-uk]

Thanks. Commit link af01b2f16

[psychocrypt]

I will check it, maybe I will add an option that the user can choose between both scratchpad patterns to fine tune the miner.