drm/amdgpu: clear the warning unsigned compared against 0 for xcp_id

This greater-than-or-equal-to-zero comparison of an unsigned value is always true. fpriv->xcp_id >= 0U

Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Reviewed-by: Tim Huang <Tim.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>