drm/amd/display: Fix Coverity INTERGER_OVERFLOW within construct_integrated_info

[Why]
For substrcation, coverity reports integer overflow
warning message when variable type is uint32_t.

[How]
Change varaible type to int32_t.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>