drm/amd/display: remove unused variable res_pool

With gcc and W=1, there is this error
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm_mst_types.c:1214:31:
  error: variable ‘res_pool’ set but not used [-Werror=unused-but-set-variable]
 1214 |         struct resource_pool *res_pool;
      |                               ^~~~~~~~

Since res_pool is unused, remove it.
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c

@@ -1211,7 +1211,6 @@ static int pre_compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
 	bool computed_streams[MAX_PIPES];
 	struct amdgpu_dm_connector *aconnector;
 	struct drm_dp_mst_topology_mgr *mst_mgr;
-	struct resource_pool *res_pool;
 	int link_vars_start_index = 0;
 	int ret = 0;
 
@@ -1220,7 +1219,6 @@ static int pre_compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
 
 	for (i = 0; i < dc_state->stream_count; i++) {
 		stream = dc_state->streams[i];
-		res_pool = stream->ctx->dc->res_pool;
 
 		if (stream->signal != SIGNAL_TYPE_DISPLAY_PORT_MST)
 			continue;