drm/amd/display: Fix signed/unsigned comparison mismatches

drm/amd/display: Fix signed/unsigned comparison mismatches

[Why]
Address signed/unsigned comparison warnings in DC paths
to keep builds warning-clean and improve type safety at comparison boundaries.
Most warnings came from signed loop/index temporaries compared against unsigned
counters (for example pipe_count, num_states, and resource-cap counters), plus a
small number of mixed signed/unsigned checks in writeback and clock-related assertions.

[How]
Aligned iterator and temporary variable types with the semantic type of the compared
bounds. Used unsigned indices for loops bounded by unsigned counters, and retained signed
types where values are semantically signed (for example arithmetic with sentinel or signed
intermediate values). Where mixed signed/unsigned comparisons are intentional, applied
explicit boundary casts or split assertions (for example non-negative signed-cap
checks before unsigned comparisons) instead of broad type changes.

No functional behavior changes are intended; this is a warning-resolution and
type-alignment cleanup.

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>