drm/amd/display: Remove useless assignments

[WHAT & HOW]
"split_pipe" are assigned to test_pipe and then immediately are updated
to other values. The same also applies to "status" as well.

Similarly, "id", "dwb" and "unused_dpps" are assigned but the functions
immediately return, and thus they have no effects.

As a results, the assignments removed.

This fixes 5 UNUSED_VALUE issues reported by Coverity.

Reviewed-by: Rodrigo Siqueira <[e-mail]>
Signed-off-by: Alex Hung <[e-mail]>
Signed-off-by: Roman Li <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/dml2/dml2_wrapper.c

···
 				p->cur_display_config->output.OutputEncoder[0], p->cur_mode_support_info->DSCEnabled[0]) - 1;
 
 			if (odms_needed <= unused_dpps) {
-				unused_dpps -= odms_needed;
-
 				if (odms_needed == 1) {
 					p->new_policy->ODMUse[0] = dml_odm_use_policy_combine_2to1;
 					optimization_done = true;

drivers/gpu/drm/amd/display/dc/gpio/gpio_service.c

···
 	case GPIO_ID_GPIO_PAD:
 	break;
 	default:
-		id = GPIO_ID_HPD;
 		ASSERT_CRITICAL(false);
 		return NULL;
 	}

drivers/gpu/drm/amd/display/dc/hwss/dcn10/dcn10_hwseq.c

···
 		r2 = test_pipe->plane_res.scl_data.recout;
 		r2_r = r2.x + r2.width;
 		r2_b = r2.y + r2.height;
-		split_pipe = test_pipe;
 
 		/**
 		 * There is another half plane on same layer because of

drivers/gpu/drm/amd/display/dc/hwss/dcn30/dcn30_hwseq.c

···
 	}
 	/*following is the original: warmup each DWB's mcif buffer*/
 	for (i = 0; i < num_dwb; i++) {
-		dwb = dc->res_pool->dwbc[wb_info[i].dwb_pipe_inst];
 		mcif_wb = dc->res_pool->mcif_wb[wb_info[i].dwb_pipe_inst];
 		/*warmup is for VM mode only*/
 		if (wb_info[i].mcif_buf_params.p_vmid == 0)

drivers/gpu/drm/amd/display/dc/hwss/dcn401/dcn401_hwseq.c

···
 		r2 = test_pipe->plane_res.scl_data.recout;
 		r2_r = r2.x + r2.width;
 		r2_b = r2.y + r2.height;
-		split_pipe = test_pipe;
 
 		/**
 		 * There is another half plane on same layer because of

drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c

···
 
 			/* 5. check CR done*/
 			if (dp_is_cr_done(lane_count, dpcd_lane_status)) {
-				status = LINK_TRAINING_SUCCESS;
 				break;
 			}