drm/amd/display: remove set but not used variable 'ds_port'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link_dp.c: In function dp_wa_power_up_0010FA:
drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link_dp.c:2320:35: warning:
 variable ds_port set but not used [-Wunused-but-set-variable]

It is never used, so can be removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>