drm/amdgpu/display: fix compiler errors [-Werror,-Wparentheses-equality]

Remove extraneous parentheses around the comparison
to silence this warning

Signed-off-by: Pratik Vishwakarma <Pratik.Vishwakarma@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>