drm/amd/display: Use pipe_count for num of opps

[Why]
There is one opp per pipe. For certain RN parts, the fourth pipe is disabled, so there is no opp for it.
res_cap->num_opp is hardcoded to 4, so if we use that to iterate over opps we will crash.

[How]
Use the pipe_count value instead, which is not hardcoded and so will have the correct number.
Signed-off-by: Noah Abradjian <noah.abradjian@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c

@@ -1357,7 +1357,7 @@ static void dcn20_update_dchubp_dpp(
 		// MPCC inst is equal to pipe index in practice
 		int mpcc_inst = pipe_ctx->pipe_idx;
 		int opp_inst;
-		int opp_count = dc->res_pool->res_cap->num_opp;
+		int opp_count = dc->res_pool->pipe_count;
 
 		for (opp_inst = 0; opp_inst < opp_count; opp_inst++) {
 			if (dc->res_pool->opps[opp_inst]->mpcc_disconnect_pending[mpcc_inst]) {