Removed unnecessary branching in dot products

[shakedregev]

Description

The current branching statement introduces errors on some machine.
Partially addresses: #468

Proposed changes

Removed the branching.

Checklist

• All tests pass (make test and make test_install per testing instructions). Code tested on
  • CPU backend
  • CUDA backend
  • HIP backend
• I have manually run the non-experimental examples and verified that residuals are close to machine precision. (In your build directory run: ./examples/<your_example>.exe -h to get instructions how to run examples). Code tested on:
  • CPU backend
  • CUDA backend
  • HIP backend
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows Re::Solve style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• Minor PR, no changelog

[pelesh]

There was a performance reason why @kswirydo has implemented a separate kernel for certain sizes of multiple dot products. I would rather check what errors are showing up and on what machines, first. It may be a fixable bug.