Evaluate_PSNR_SSIM.m and Warning ignore of main code

[Davorking]

I've spotted some subtle issues that may need to be taken care of.

1. Evaluate_PSNR_SSIM.m appears to be using ./HR directory for reading HR images in order to compute PSNR and SSIM value. However, according to the Readme, the correct directory actually should be ./benchmark/HR/.
   Line 34 and Line 41 should add an additional './benchmark' parameter to fullfile() function.

2. The whole warning suppression module import and usage seems completely unnecessary, just change line 206 of ./ops/OSA.py to
   grid = torch.stack(torch.meshgrid(pos, pos, indexing="ij")) the warning would go away.