Perf Drop when redundant code is removed from tt-fabric FVC Producer

[ubcheema]

In FVC producer logic, fvc_out_wrptr can be removed as it is redundant.

The one place where it is being used, the value can be calculated as:
local_pull_request->pull_request.wr_ptr = inc_ptr_with_wrap(fvc_out_rdptr, words_available)

However, doing this drops bandwidth by ~14%.
This drop in perf needs to be properly understood.