drm/amd/display/dc/core/dc_link_ddc: Remove unnecessary conversion to bool

Fix the following coccicheck warnings:

./drivers/gpu/drm/amd/display/dc/core/dc_link_ddc.c:544:34-39: WARNING:
conversion to bool not needed here.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>