drm/amd/display: Remove redundant macro of refresh rate

[Why&How]
Found that we add redundant macro on refresh rate when calculating vtotal,
so we remove it.

Reviewed-by: Robin Chen <robin.chen@amd.com>
Signed-off-by: Weiguang Li <wei-guang.li@amd.com>
Signed-off-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>