drm/amd/display: use true, false for bool variable in dc_link_ddc.c

Fixes coccicheck warning:

drivers/gpu/drm/amd/display/dc/core/dc_link_ddc.c:593:6-9: WARNING: Assignment of 0/1 to bool variable

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>