drm/amd/display: Remove unused variables in dcn21_hwseq.c

Fix the below compiler error:

drivers/gpu/drm/amd/amdgpu/../display/dc/dcn21/dcn21_hwseq.c:229:11: error: unused variable 'otg_inst' [-Werror,-Wunused-variable]
        uint32_t otg_inst = pipe_ctx->stream_res.tg->inst;
                 ^
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn21/dcn21_hwseq.c:226:20: error: unused variable 'cmd' [-Werror,-Wunused-variable]
        union dmub_rb_cmd cmd;

Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Jerry Zuo <jerry.zuo@amd.com>
Cc: Yongqiang Sun <yongqiang.sun@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Yongqiang Sun <Yongqiang.Sun@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn21/dcn21_hwseq.c

@@ -223,10 +223,8 @@ bool dcn21_set_backlight_level(struct pipe_ctx *pipe_ctx,
 		uint32_t backlight_pwm_u16_16,
 		uint32_t frame_ramp)
 {
-	union dmub_rb_cmd cmd;
 	struct dc_context *dc = pipe_ctx->stream->ctx;
 	struct abm *abm = pipe_ctx->stream_res.abm;
-	uint32_t otg_inst = pipe_ctx->stream_res.tg->inst;
 	struct panel_cntl *panel_cntl = pipe_ctx->stream->link->panel_cntl;
 
 	if (dc->dc->res_pool->dmcu) {