drm/amd/display: Fix gcc unused variable warning

GCC reports the following warning with W=1:

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link_dp.c:3635:17:
warning:
 variable ‘status’ set but not used [-Wunused-but-set-variable]
  3635 |  enum dc_status status = DC_ERROR_UNEXPECTED;
       |                 ^~~~~~

The variable should be used for error check, let's fix it.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>