drm/amd/display: Fix multiple compiler warnings

drm/amd/display: Fix multiple compiler warnings

[Why]
Unreachable Code;
Copy Constructor Deleted;
Local Declaration Hides Parameter;
Local Declaration Hides Outer Scope;
Uninitialized or Suspicious Memory Use.

[How]
- Removed or refactored unreachable code paths
- Ensured proper copy constructors in C++ classes
- Renamed local variables that shadowed function parameters
- Renamed inner loop/block variables to avoid shadowing outer scope
  Fixed in 8 files across several FPU layers
  Also fixed in color_gamma and cs_funcs modules
- Reordered guard conditions to validate pipe type before accessing stream
- Ensures safe memory access patterns in DC DMUB service layer

All changes maintain backward compatibility and preserve functional behavior.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Gaghik Khachatrian <gaghik.khachatrian@amd.com>
Signed-off-by: James Lin <pinglei.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>