Replaced parameter B with the total parameters calculated outside of the kernel

[ChrisDryden]

Similar to this CR: https://github.com/karpathy/llm.c/pull/520 but with some more opinionated variable name changes, since N is already taken, I renamed it to total_parameters, but open to any other options

[karpathy]

Does this actually make difference? Maybe I'd prefer the more consistent naming scheme.