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: NHarry Wentland <harry.wentland@amd.com>
Signed-off-by: NPu Lehui <pulehui@huawei.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c

@@ -3675,6 +3675,10 @@ bool dp_retrieve_lttpr_cap(struct dc_link *link)
 				DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV,
 				lttpr_dpcd_data,
 				sizeof(lttpr_dpcd_data));
+		if (status != DC_OK) {
+			dm_error("%s: Read LTTPR caps data failed.\n", __func__);
+			return false;
+		}
 
 		link->dpcd_caps.lttpr_caps.revision.raw =
 				lttpr_dpcd_data[DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV -