drm/amd/display: remove useless if/else

Fix the following coccinelle report:

./drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c:1367:3-5:
WARNING: possible condition with no effect (if == else)

Both branches are the same, so remove the if/else altogether.

Fixes: 81875979 ("drm/amd/display: Remove extra pairs of parentheses in dce_calcs.c")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>