drm/amd/display: Assign disp_cfg_index_max when dml21

[WHY & HOW]
The assignment of disp_cfg_index_max is missed and should be
assigned to __DML2_WRAPPER_MAX_STREAMS_PLANES__.

Fixes: 55ec7679 ("drm/amd/display: Limit array index according to architecture")
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dml2/dml2_dc_resource_mgmt.c

@@ -1058,6 +1058,7 @@ bool dml2_map_dc_pipes(struct dml2_context *ctx, struct dc_state *state, const s
 
 		ODMMode = (const unsigned int *)odm_mode_array;
 		DPPPerSurface = (const unsigned int *)dpp_per_surface_array;
+		disp_cfg_index_max = __DML2_WRAPPER_MAX_STREAMS_PLANES__;
 	} else {
 		ODMMode = (unsigned int *)disp_cfg->hw.ODMMode;
 		DPPPerSurface = disp_cfg->hw.DPPPerSurface;