[BC-breaking] Fix ssim run on cuda 2532

[sadra-barikbin]

Fixes #2532

Description:

• Recoded update/compute methods : [BC-breaking] compute now return float instead of Tensor
• Fix for master to be able to run on cuda

Check list:

• New tests are added (if a new feature is added)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (if required)

[vfdev-5]

Thanks @sadra-barikbin