drm/amd/display: Remove incorrect ASSERT check for link_enc

[Why]
It's possible that we don't have a link encoder assignment if the
context is NULL but we're calling dc_add_stream_to_ctx from DM directly.

Link encoder assignment will happen later after global validation
runs with fast_validate = false.

[How]
Remove the ASSERTION. We already guard against NULL link_enc.
Reviewed-by: Michael Strauss <Michael.Strauss@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c

@@ -1246,10 +1246,9 @@ static void get_pixel_clock_parameters(
 	pixel_clk_params->requested_pix_clk_100hz = stream->timing.pix_clk_100hz;
 
 	link_enc = link_enc_cfg_get_link_enc(link);
-	ASSERT(link_enc);
-
 	if (link_enc)
 		pixel_clk_params->encoder_object_id = link_enc->id;
+
 	pixel_clk_params->signal_type = pipe_ctx->stream->signal;
 	pixel_clk_params->controller_id = pipe_ctx->stream_res.tg->inst + 1;
 	/* TODO: un-hardcode*/