MIOpenConvBwdWrWS2.cl restore performance by unroll loop
MIOpenConvBwdWrWS2.cl restore performance by unroll loop

ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen