drm/amd/display: remove possible condition with no effect (if == else)

Conditional statements have no effect to next process.So remove it.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2028


Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>